[media] staging/media/solo6x10/v4l2-enc.c: fix error-handling

The return values of copy_to_user() and copy_from_user() cannot be negative.
Found using the following semantich patch:
<spml>
@exists@
identifier ret;
statement S;
expression E;
@@
(
* ret = copy_to_user(...);
|
* ret = copy_from_user(...);
)
... when != ret = E
    when != if (ret) { <+... ret = E; ...+> }
* if (ret < 0)
  S
</spml>

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>