cnss2: Ignore logging MHI IDLE notification

MHI will only send IDLE notification once it enters M2 state which
is not interested by driver at all. Ignore even printing it to avoid
flushing log buffer.

Change-Id: I1094b08f97a5883836d3951ecaaac0c64b1aa9d2
Signed-off-by: Yue Ma <yuem@codeaurora.org>