MAINTAINERS: BCACHE: Kent Overstreet has changed email address

Kent's email address in MAINTAINERS seems to be invalid.
This was his last sign-off address, so use that if appropriate.

Fix the S: status entry while there.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>