mhi: core: do not notify controller of RDDM EE more than once

MHI core driver ends up notifying controller of RDDM EE
more than once in cases where back to back transitions such as
FORCE_RDDM followed by POWER_OFF are initiated.

Change-Id: I2fe854f04c3fac7bee124f6270b88e5154facb0b
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>