mmc: block: fixed NULL pointer dereference
mmc: block: fixed NULL pointer dereference

We already check for ongoing async transfers when handling discard
requests, but not in mmc_blk_issue_flush().  This patch fixes that
omission.

Tested with an SDHCI controller and eMMC4.41.

Signed-off-by: Jaehoon Chung <6d67df43a1b10a02c7c04e8346f9d9ca207335e5@samsung.com>
Signed-off-by: Kyungmin Park <504c23c4986a3760712724894be3105092c27331@samsung.com>
Acked-by: Per Forlin <eef895a6d2c8ac90ff468c9f412501c535a132ff@linaro.org>
Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@kernel.org>
Signed-off-by: Chris Ball <6ca7faee6ca9a094b1ee341f11b840a5608a8746@laptop.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas