performance/md-cache: set right error check in {f}getxattr_cbk()

Currently mdc_{f}getxattr_cbk() check(s) for a non-zero value to
determine if any cache update has to be performed. Right from
posix xlator, op_ret has a positive value upon success and -1 upon
failure. This patch sets right the check in getxattr callbacks so
that xattr cache update happens for successful calls.

Change-Id: Ifa5ec38bdf7e3dc095de9a56d91559b13cd9e8b6
BUG: 1208784
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/10127
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra Talur <rtalur@redhat.com>

xlators/performance/md-cache/src/md-cache.c

@@ -1764,7 +1764,7 @@ mdc_getxattr_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 {
         mdc_local_t  *local = NULL;
 
-        if (op_ret != 0)
+        if (op_ret < 0)
                 goto out;
 
         local = frame->local;
@@ -1826,7 +1826,7 @@ mdc_fgetxattr_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 {
         mdc_local_t  *local = NULL;
 
-        if (op_ret != 0)
+        if (op_ret < 0)
                 goto out;
 
         local = frame->local;