Add #! to 'am' shell script

Shell script needs to start with #! for exec().

Bug 10606037

Change-Id: I594da6f0433e838dcf5b45b991188ceaa52d9bd1
diff --git a/cmds/am/am b/cmds/am/am
index c823634..1d426bc 100755
--- a/cmds/am/am
+++ b/cmds/am/am
@@ -1,3 +1,5 @@
+#!/system/bin/sh
+#
 # Script to start "am" on the device, which has a very rudimentary
 # shell.
 #