MAINTAINERS: remove drivers/platform/msm/

This subdirectory entry was added by commit 8a5700cd ("MAINTAINERS:
add drivers/platform/msm to MSM subsystem") back in 2011, but I could
not find any trace of that directory being ever added to the repository.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Cc: Kenneth Heitke <kheitke@codeaurora.org>
Acked-by: David Brown <davidb@codeaurora.org>
Cc: Daniel Walker <dwalker@fifo99.com>
Cc: Bryan Huntsman <bryanh@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>