mmc: Fix err-handling path when there is active Discard (DCMD)

In case of Discard requests, currently the error handler was
not waking up the cmdq-thread which is waiting for completion
even of discard requests. This was happening when the error
requests is non-discard requests.
So this patch adds a way to wake up the issue thread waiting
on discard completion event

Change-Id: Ia663a2cf41004ce18a409b5a29f715e672c8a7ae
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>