mantis: Fix typo in mantis_hif.c

Correct typo "Adater" to "Adapter" in
drivers/media/dvb/mantis/mantis_hif.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>