net: mdio-mux-mmioreg: Can handle 8/16/32 bits registers

This patch fix an old information that mdio-mux-mmioreg can only handle
8bit registers.
This is not true anymore.
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/Kconfig

@@ -85,7 +85,7 @@ config MDIO_BUS_MUX_MMIOREG
 	  parent bus.  Child bus selection is under the control of one of
 	  the FPGA's registers.
 
-	  Currently, only 8-bit registers are supported.
+	  Currently, only 8/16/32 bits registers are supported.
 
 config MDIO_CAVIUM
 	tristate