MAINTAINERS: update bt8xx gpio F: patterns

Commit c103de24 ("gpio: reorganize drivers") renamed the file, update
the pattern.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Michael Buesch <m@bues.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>