mmc: core: continue to wait, when unblocked by signal

Mmc thread is waiting for one of following events occurs:
- current running request completion (is_done_rcv)
- new request notification arrived (is_new_req)
- urgent request notification arrived (is_urgent)
or the thread received a signal. In this case none of described events
happened.

This change process the case, when mmc thread was unblocked from wait by
signal, for example system shutdown flow.

Change-Id: I0b4f0cefedc839640c162ad3cdb011d13daaee0c
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>