RDMA/cm: Use specific keyword to check define

There is a specific define keyword to check if define exists or not,
let's use it instead of open-coded variant.

Link: https://lore.kernel.org/r/20191020071559.9743-3-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
diff --git a/drivers/infiniband/core/cm_msgs.h b/drivers/infiniband/core/cm_msgs.h
index 3d16d614..0a9e2d3f 100644
--- a/drivers/infiniband/core/cm_msgs.h
+++ b/drivers/infiniband/core/cm_msgs.h
@@ -31,7 +31,7 @@
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS THE
  * SOFTWARE.
  */
-#if !defined(CM_MSGS_H)
+#ifndef CM_MSGS_H
 #define CM_MSGS_H
 
 #include <rdma/ib_mad.h>