MAINTAINERS: SI4713: fix file pattern

Commit c937ca03

 ("[media] MAINTAINERS: Add maintainer entry for
si4713 FM transmitter driver") typoed the pattern, fix it.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>