r8169: prevent bit sign expansion error in mdio_write

Oops.

The current code does not like being given an u16 with the highest
bit set as an argument to mdio_write. Let's enforce a correct range of
values for both the register address and value (resp. 5 and 16 bits).

The callers are currently left as-is.
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>

drivers/net/r8169.c

@@ -470,7 +470,7 @@ static void mdio_write(void __iomem *ioaddr, int reg_addr, int value)
 {
 	int i;
 
-	RTL_W32(PHYAR, 0x80000000 | (reg_addr & 0xFF) << 16 | value);
+	RTL_W32(PHYAR, 0x80000000 | (reg_addr & 0x1f) << 16 | (value & 0xffff));
 
 	for (i = 20; i > 0; i--) {
 		/*
@@ -487,7 +487,7 @@ static int mdio_read(void __iomem *ioaddr, int reg_addr)
 {
 	int i, value = -1;
 
-	RTL_W32(PHYAR, 0x0 | (reg_addr & 0xFF) << 16);
+	RTL_W32(PHYAR, 0x0 | (reg_addr & 0x1f) << 16);
 
 	for (i = 20; i > 0; i--) {
 		/*
@@ -495,7 +495,7 @@ static int mdio_read(void __iomem *ioaddr, int reg_addr)
 		 * the specified MII register.
 		 */
 		if (RTL_R32(PHYAR) & 0x80000000) {
-			value = (int) (RTL_R32(PHYAR) & 0xFFFF);
+			value = RTL_R32(PHYAR) & 0xffff;
 			break;
 		}
 		udelay(25);