V4L/DVB (5900): usbvision: fix bugs [sg]_register functions

s_register was assigning the return code to (unsigned)reg->val, rather than
errCode, which it what it would return.  Except reg->val can't be < 0, so it
would never actually return an error.

g_register never actually put the value it read into reg->val.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>