msm: pcie: update the flow to avoid unlocking mutex twice

In workqueue function for PCIe wake IRQ, the mutex is unlocked
twice in some case. Update the flow in this function to avoid
unlock the same mutex twice.

CRs-fixed: 669457
Change-Id: Ic567d463bcc20d022c13a3e67740ceacb03174ee
Signed-off-by: Yan He <yanhe@codeaurora.org>