get_maintainer.pl: add -mpath=<path or file> for MAINTAINERS file location

Add the ability to have an override for the location of the MAINTAINERS
file.

Miscellanea:

o Properly indent a few lines with leading spaces

Link: http://lkml.kernel.org/r/a86e69195076ed3c4c526fddc76b86c28e0a1e37.camel@perches.com


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