ext4: Change the wrong param comment for ext4_trim_all_free

at ext4_trim_all_free() comment, there is no longer an @e4b parameter,
instead it is @group.

Reported-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 73c2540..04a3d92 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4811,7 +4811,7 @@
 /**
  * ext4_trim_all_free -- function to trim all free space in alloc. group
  * @sb:			super block for file system
- * @e4b:		ext4 buddy
+ * @group:		group to be trimmed
  * @start:		first group block to examine
  * @max:		last group block to examine
  * @minblocks:		minimum extent block count