V4L/DVB: pvrusb2: remove unneeded NULL checks

We dereference "maskptr" unconditionally at the start of the function
and also inside the call to parse_tlist() towards the end of the
function.  This function is called from store_val_any() and it always
passes a non-NULL pointer.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>