sfc: Fix dependency for SFC_MTD

Randy Dunlap found that SFC_MTD was selected when sfc was built-in and
the MTD core was a module.  Don't allow that combination.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Acked-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/sfc/Kconfig

@@ -14,7 +14,7 @@ config SFC
 	  will be called sfc.
 config SFC_MTD
 	bool "Solarflare Solarstorm SFC4000 flash MTD support"
-	depends on SFC && MTD
+	depends on SFC && MTD && !(SFC=y && MTD=m)
 	default y
 	help
 	  This exposes the on-board flash memory as an MTD device (e.g.