dm: do not reuse dm_blk_ioctl block_device input as local variable
dm: do not reuse dm_blk_ioctl block_device input as local variable

(Ab)using the @bdev passed to dm_blk_ioctl() opens the potential for
targets' .prepare_ioctl to fail if they go on to check the bdev for
!NULL.

Fixes: e56f81e0b01e ("dm: refactor ioctl handling")
Reported-by: Junichi Nomura <3576fcbd7ffa3776a92ac17fc90ba38e23f75e95@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <85e533f2e78486213c4d69f71462342ec0c62734@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs