Use REQ_OP_READ and REQ_OP_WRITE macros instead of READ and WRITE.  They
have the same value, but the block layer uses REQ_OP so bufio should
too.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>