autotest: cras_utils: Fix pylint error

BUG=None
TEST=run_pylint client/cros/audio/

Change-Id: I067c53080b397a1ae4292d75a182d3e9c782f0a3
Reviewed-on: https://chromium-review.googlesource.com/273460
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
diff --git a/client/cros/audio/cras_utils.py b/client/cros/audio/cras_utils.py
index bd1c3d5..5034b38 100644
--- a/client/cros/audio/cras_utils.py
+++ b/client/cros/audio/cras_utils.py
@@ -12,12 +12,22 @@
 _CRAS_TEST_CLIENT = '/usr/bin/cras_test_client'
 
 def playback(*args, **kargs):
-    """A helper function to execute the playback_cmd."""
+    """A helper function to execute the playback_cmd.
+
+    @param args: args passed to playback_cmd.
+    @param kargs: kargs passed to playback_cmd.
+
+    """
     cmd_utils.execute(playback_cmd(*args, **kargs))
 
 
 def capture(*args, **kargs):
-    """A helper function to execute the capture_cmd."""
+    """A helper function to execute the capture_cmd.
+
+    @param args: args passed to capture_cmd.
+    @param kargs: kargs passed to capture_cmd.
+
+    """
     cmd_utils.execute(capture_cmd(*args, **kargs))
 
 
@@ -29,8 +39,11 @@
                           playback raw audio from the stdin.
     @param block_size: the number of frames per callback(dictates latency).
     @param duration: seconds to playback
+    @param channels: number of channels.
     @param rate: the sampling rate
 
+    @returns: The command args put in a list of strings.
+
     """
     args = [_CRAS_TEST_CLIENT]
     args += ['--playback_file', playback_file]
@@ -52,8 +65,11 @@
     @param duration: seconds to record. If it is None, duration is not set,
                      and command will keep capturing audio until it is
                      terminated.
+    @param channels: number of channels.
     @param rate: the sampling rate.
 
+    @returns: The command args put in a list of strings.
+
     """
     args = [_CRAS_TEST_CLIENT]
     args += ['--capture_file', capture_file]
@@ -67,7 +83,13 @@
 
 
 def loopback(*args, **kargs):
-    """A helper function to execute loopback_cmd."""
+    """A helper function to execute loopback_cmd.
+
+    @param args: args passed to loopback_cmd.
+    @param kargs: kargs passed to loopback_cmd.
+
+    """
+
     cmd_utils.execute(loopback_cmd(*args, **kargs))
 
 
@@ -79,6 +101,8 @@
     @param duration: seconds to record.
     @param rate: the sampling rate.
 
+    @returns: The command args put in a list of strings.
+
     """
     args = [_CRAS_TEST_CLIENT]
     args += ['--loopback_file', output_file]