mhi: core: move PM state to SYS_ERROR if the event arrives before RDDM

Allow a move to SYS_ERROR if its arrival precedes that of an
RDDM entry notification so that the core driver remains inactive
for that period in its anticipation.

Change-Id: I6222430f34528f8b5f4c3d3d544ebc359ed05708
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>