mhi: core: block fast suspends on controller device bus vote

Currently only a pending packets check is used to block fast
suspends. Since it does not exactly reflect what the core
driver intends to do, allow a bus vote to the controller device
to block fast suspends as well.

Change-Id: I31266d296e855027f6b49b2dcfe4606bb48ac221
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>