bus: mhi: core: Address pending BW requests for legacy mode

It cannot be guaranteed that certain legacy mode controllers stay
in M0 while a BW request is being processed. Ensure that those
pending BW requests are addressed when M0 entry occurs after a BW
request is processed but not responded to.

Change-Id: I6132116fae76fa10477aa7061c24f3ff5ac60a34
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>