security: avoid calling a NULL function pointer in drivers/video/tvaudio.c

security: avoid calling a NULL function pointer in drivers/video/tvaudio.c

commit 5ba2f67afb02c5302b2898949ed6fc3b3d37dcf1 upstream

NULL function pointers are very bad security wise. This one got caught by
kerneloops.org quite a few times, so it's happening in the field....

Fix is simple, check the function pointer for NULL, like 6 other places
in the same function are already doing.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>