mmc: core: Return the error if command queue request fails

command-queue request may fail during preparation/issuing in some
cases. In case if it fails, the error code needs to be propagated back
to the function which initiated the request so that the request can be
handled appropriately.

Change-Id: Ia6946c14f0c106fb30bd70ca5c9e600c516fdf55
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>