sfc: Fix type of FALCON_SPI_MAX_LEN

FALCON_SPI_MAX_LEN has type size_t while other SPI lengths have type
unsigned int.  This results in warnings from min() on 64-bit
architectures where they are different.  Add a cast to make it match.

From: Steve Hodgson <shodgson@solarflare.com>
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/net/sfc/falcon.c

@@ -1605,7 +1605,7 @@ void falcon_fini_interrupt(struct efx_nic *efx)
  **************************************************************************
  */
 
-#define FALCON_SPI_MAX_LEN sizeof(efx_oword_t)
+#define FALCON_SPI_MAX_LEN ((unsigned) sizeof(efx_oword_t))
 
 /* Wait for SPI command completion */
 static int falcon_spi_wait(struct efx_nic *efx)