Revert "mhi: core: Force PM state to M0 while processing BW scaling event"

This reverts commit 6beaad9d. In case
low priority work processes the empty bw scaling event it returns
without decrementing the dev wake count. This results into assert
in case of a esoc power off.

Change-Id: I4948ec53a76d18a337281a993b11225dfc907f2e
Signed-off-by: Siva Kumar Akkireddi <sivaa@codeaurora.org>