[media] staging/media/solo6x10: Use PTR_RET rather than if(IS_ERR(...)) + PTR_ERR

Found with coccicheck.
The semantic patch that makes this change is available
in scripts/coccinelle/api/ptr_ret.cocci.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>