mmc: core: fix block request queue hang during data crc errors

When data CRC errors occur during write transactions, mmc
block layer queries the card for successful writes. If the card
reports bytes requested as bytes successfully written, the mmc
block layer will end the request with blk_end_request(). If there
is a following async request pending for execution, the request
is thrown away while handling CRC errors leading to hang in
request queue. The hang is visible when user issues a sync()
system call.

The sequence of events are as follows -

mmcqd -> fetch a request -> send it to host driver -> fetch another
request -> wait for previous request to complete -> previous request
is in error -> skip sending current request to host driver and
do error handling for previous request in error.

During the last step, after error handling is completed the mmc
block layer does not requeue the current request which is skipped
and hence the request is infinitely stuck in the driver.

Change-Id: I9528fbe3ccb5b723fcd0793f86cca43906c4c29c
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>