ata: define AC_ERR_OK

commit 25937580a5065d6fbd92d9c8ebd47145ad80052e upstream.

Since we will return enum ata_completion_errors from qc_prep in the next
patch, let's define AC_ERR_OK to mark the OK status.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/libata.h b/include/linux/libata.h
index e752368..6346272 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -486,6 +486,7 @@
 };
 
 enum ata_completion_errors {
+	AC_ERR_OK		= 0,	    /* no error */
 	AC_ERR_DEV		= (1 << 0), /* device reported error */
 	AC_ERR_HSM		= (1 << 1), /* host state machine violation */
 	AC_ERR_TIMEOUT		= (1 << 2), /* timeout */