media: si2157: ensure wait_status is initialized

smatch reports wait_status is uninitialized, because smatch cannot assume
the loop body is ever executed.

Clarify the code so that wait_status is retrieved at least once.

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