mmc: block: Fix is_waiting_last_req set incorrectly

Commit 15520111 ("mmc: core: Further fix thread wake-up") allowed a
queue to release the host with is_waiting_last_req set to true. A queue
waiting to claim the host will not reset it, which can result in the
queue getting stuck in a loop.

Fixes: 15520111 ("mmc: core: Further fix thread wake-up")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>