MAINTAINERS: fix tape driver file mappings

The masks for the st and osst tape drivers in MAINTAINERS are too
broad and include unrelated files. Make the file list accurate so that
maintainers of these drivers aren't bothered with unrelated work.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Willem Riede <osst@riede.org>
Cc: Kai Mäkisara <Kai.Makisara@kolumbus.fi>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>