msm: ipa: Unlock mutex before voting PCIe clocks

This fix unlocks the mutex before calling into MHI api to vote
PCIE clocks, to make sure there is no dead lock.

Change-Id: I08b8b5b39c0de9ef7c542173b63cdc8567337440
Acked-by: Jyothi Jayanthi <jyothij@qti.qualcomm.com>
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>