[hermon] Add missing __attribute__ (( packed ))

On 64-bit builds, MLX_DECLARE_STRUCT() produces a structure that is
always a multiple of 64 bits long, causing the HCR structure to be
over-length by one dword.  This in turn causes hermon_cmd() to write
beyond the end of the HCR, which causes commands to fail.

Reported-by: Itay Gazit <itayg@mellanox.co.il>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/infiniband/mlx_bitops.h

 		uint8_t bytes[ sizeof ( struct _structure ## _st ) / 8 ];    \
 		uint32_t dwords[ sizeof ( struct _structure ## _st ) / 32 ]; \
 		struct _structure ## _st *dummy[0];			     \
-	    } u;							     \
-	}
+	    } __attribute__ (( packed )) u;				     \
+	} __attribute__ (( packed ))
 
 /** Get pseudo_bit_t structure type from wrapper structure pointer */
 #define MLX_PSEUDO_STRUCT( _ptr )					     \