spi: spi_qsd: serve set_cs call only for valid device status

when set_cs() is called by framework, first check the device suspend
status and if not suspended then proceed for register access. Let system
suspend call SPI runtime suspend but make sure set_cs doesn't race with
it by holding the mutex.

Change-Id: Id6d05ac37227bf3358438eeedf279ddd1c9aab8b
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>