spi_qsd: Fix SPI L2 Crash

Message queue is scheduled to process
SPI messages during system suspend
state which leads to crash.

This patch make sure all the messages
in queue are processed before system
suspends.

CRs-Fixed: 593658
Change-Id: I722f24fcee4a1d2bbfee4341c8bc6c36ff9e1ec8
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>