msm: ipa3: unlock uC spinlock before injecting DMA_TASK

Fix for scheduling while atomic bug in case uC GSI stop channel
is stuck in STOP_IN_PROG. Before injecting DMA_TASK and sleeping release
uC spinlock.

Change-Id: I19d5291f16a729c57adc6244ab79ebae9ce927e7
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>