target/iblock: Fix WCE=1 + DPOFUA=1 backend WRITE regression

This patch fixes a regression bug introduced in v3.9-rc1 where if the
underlying struct block_device for a IBLOCK backend is configured with
WCE=1 + DPOFUA=1 settings, the rw = WRITE assignment no longer occurs
in iblock_execute_rw(), and rw = 0 is passed to iblock_submit_bios()
in effect causing a READ bio operation to occur.

The offending commit is:

commit d0c8b259f8970d39354c1966853363345d401330
Author: Nicholas Bellinger <nab@linux-iscsi.org>
Date:   Tue Jan 29 22:10:06 2013 -0800

    target/iblock: Use backend REQ_FLUSH hint for WriteCacheEnabled status

Note the WCE=1 + DPOFUA=0, WCE=0 + DPOFUA=1, and WCE=0 + DPOFUA=0 cases
are not affected by this regression bug.

Reported-by: Chris Boot <bootc@bootc.net>
Tested-by: Chris Boot <bootc@bootc.net>
Reported-by: Hannes Reinecke <hare@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_iblock.c

@@ -615,6 +615,8 @@ iblock_execute_rw(struct se_cmd *cmd)
 				rw = WRITE_FUA;
 			else if (!(q->flush_flags & REQ_FLUSH))
 				rw = WRITE_FUA;
+			else
+				rw = WRITE;
 		} else {
 			rw = WRITE;
 		}