get_maintainer.pl: reduce need for command-line option -f

If a vcs is used, look to see if the vcs tracks the file specified and
so the -f option becomes optional.

Link: http://lkml.kernel.org/r/7c86a8df0d48770c45778a43b6b3e4627b2a90ee.1469746395.git.joe@perches.com


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>