checkpatch: update git commit message

The git commit message can be confusing,

Try to clarify the message a bit to reduce the confusion when emitted.

Show the correct form using
	Please use git commit description style 'commit <12+ chars of sha1> ("<title line>")'
and if the git commit sha1 is unique, show
the right sha1 to use with the actual title

Signed-off-by: Joe Perches <joe@perches.com>
Original-patch-by: Prarit Bhargava <prarit@redhat.com>
Tested-by: Chris Rorvick <chris@rorvick.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>