null_blk: Fix error path in module initialization
null_blk: Fix error path in module initialization

Module couldn't release resource properly during the initialization. To
fix this issue, we will clean up the proper resource before returning.

Signed-off-by: Minfei Huang <3c5fb063765d3c2eb5938ad9ebec439bc976721a@gmail.com>
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@fb.com>

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