checkpatch: yet another commit id improvement

Using \b isn't good enough to isolate what appears to be a commit id in
a commit message.

Make sure there is a space or a quote like character after a continuous
run of hexadecimal characters that could be a commit id.

Link: http://lkml.kernel.org/r/fdd22b47463a21c21132edbb8aa35e372950a1e6.1468869915.git.joe@perches.com


Signed-off-by: Joe Perches <joe@perches.com>
Cc: "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>