mmc: add the new linux-mmc mailing list to MAINTAINERS

mmc: add the new linux-mmc mailing list to MAINTAINERS

There are a number of individual MMC drivers listed in MAINTAINERS.  I
didn't modify those records.  Perhaps I should have.

Cc: <[email protected]>
Cc: Manuel Lauss <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: Pierre Ossman <[email protected]>
Cc: Pavel Pisa <[email protected]>
Cc: Jarkko Lavinen <[email protected]>
Cc: Ben Dooks <[email protected]>
Cc: Sascha Sommer <[email protected]>
Cc: Ian Molton <[email protected]>
Cc: Joseph Chan <[email protected]>
Cc: Harald Welte <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>