msm: mhi: Avoid channel read while in mhi suspend

Client may initiate read transfers when MHI state is in suspend
state. Change adds a check to prevent read transfers.

Change-Id: I51954a3493a845ed1778713c10b20400d95489a8
Signed-off-by: Subramanian Ananthanarayanan <skananth@codeaurora.org>
Signed-off-by: Gauri Joshi <gaurjosh@codeaurora.org>