scripts/get_maintainer.pl: don't search MAINTAINERS for keywords or emails

Keyword matching uses K: patterns from MAINTAINERS, so if looking for the
MAINTAINERS maintainer, don't search MAINTAINERS for pattern matches.
MAINTAINERS also has rather a lot of email addresses and is easily
searched using grep "^M:", so skip it.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>