md: bcache: io.c: fix a potential NULL pointer dereference
md: bcache: io.c: fix a potential NULL pointer dereference

bio_alloc_bioset returns NULL on failure. This fix adds a missing check
for potential NULL pointer dereferencing.

Signed-off-by: Kumar Amit Mehta <e038b94d25b48ccb2c6ad460398c5350e8279f4c@gmail.com>
Signed-off-by: Kent Overstreet <8f464ad20d7f95b5ede78c4772dc4f5cc3ffa553@google.com>

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