saa7134: Unchecked i2c_transfer function result fixed

Return value of function 'i2c_transfer' is not checked that
may cause undefined behaviour.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 2cf36ac4 ("[PATCH] v4l: 656: added support for the following cards")
Signed-off-by: Aleksandr Burakov <a.burakov@rosalinux.ru>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>