msm: mhi_dev: Acquire wakelock to avoid device suspend

Acquire wakelock in MHI ISR to avoid device
suspend while MHI device is communicating with HOST.

Change-Id: I6ae35c701502aabbc6a001e91bc7a92b2963b98d
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>