media: si2157: Check error status bit on cmd execute

Check error status bit on command execute, if error bit is
set return -EAGAIN. Ignore -EAGAIN in probe during device check.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>