drivers: ethernet: lan9250: Make interrupt mask constant unsigned

Add a 'U' suffix to the interrupt status mask passed to
lan9250_write_sys_reg() to make the constant explicitly unsigned.

This avoids signed/unsigned ambiguity and addresses a SonarQube
static analysis warning.

Signed-off-by: Gaetan Perrot <gaetan.perrot@spacecubics.com>

drivers/ethernet/eth_lan9250.c

@@ -490,7 +490,7 @@ static int lan9250_configure(const struct device *dev)
 	}
 
 	/* Clear interrupt status */
-	ret = lan9250_write_sys_reg(dev, LAN9250_INT_STS, 0xFFFFFFFF);
+	ret = lan9250_write_sys_reg(dev, LAN9250_INT_STS, 0xFFFFFFFFU);
 	if (ret < 0) {
 		return ret;
 	}