[media] pwc: Remove a bunch of bogus sanity checks / don't return EFAULT wrongly

The chances if any of these becoming NULL magically are 0% And if they
do become NULL oopsing is the right thing to do (so that the user logs a
bug with the kernel rather then with whatever app he was using).

Returning EFAULT to userspace should only be done when userspace supplies
a bad address, not on driver bugs / hw issues, so in the few cases where the
check is not bogus return something else.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>