V4L/DVB (7957): fix the roothole in av7110_av.c

direct dereferencing from user-supplied address

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>