i2c: nforce2: Use IS_ENABLED() instead of checking for built-in or module

The IS_ENABLED() macro checks if a Kconfig symbol has been enabled either
built-in or as a module, use that macro instead of open coding the same.
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-nforce2.c

@@ -127,7 +127,7 @@ static struct pci_driver nforce2_driver;
 
 /* For multiplexing support, we need a global reference to the 1st
    SMBus channel */
-#if defined CONFIG_I2C_NFORCE2_S4985 || defined CONFIG_I2C_NFORCE2_S4985_MODULE
+#if IS_ENABLED(CONFIG_I2C_NFORCE2_S4985)
 struct i2c_adapter *nforce2_smbus;
 EXPORT_SYMBOL_GPL(nforce2_smbus);