x86/MSI: improve memory usage in struct msi_desc

There's no reason to have both a 4-byte hole and 4 bytes of tail
padding.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/msi.h
+++ b/xen/include/asm-x86/msi.h
@@ -119,10 +119,9 @@ struct msi_desc {
 	};
 	struct pci_dev *dev;
 	int irq;
+	int remap_index;		/* index in interrupt remapping table */
 
 	struct msi_msg msg;		/* Last set MSI message */
-
-	int remap_index;		/* index in interrupt remapping table */
 };
 
 /*