libertas: correct packing of rxpd structure

Older Gcc compilers (3.4.5 tested) need additional hints in order to get
the packing of the rxpd structure (which contains a 16 bit union)
correct on the ARM processor.

struct txpd does not need these hints since it contains a 32 bit union
that packs naturally.
Signed-off-by: NR.J.Dunlop <rdunlop@guralp.com>
Acked-by: NDan Williams <dcbw@redhat.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/hostcmd.h

@@ -56,8 +56,8 @@ struct rxpd {
 			u8 bss_type;
 			/* BSS number */
 			u8 bss_num;
-		} bss;
-	} u;
+		} __attribute__ ((packed)) bss;
+	} __attribute__ ((packed)) u;
 
 	/* SNR */
 	u8 snr;