gpio-mcp23s08: Build I2C support even when CONFIG_I2C=m

The driver has both SPI and I2C pieces. The appropriate pieces are built based
on whether SPI and/or I2C is/are enabled. However, it was only checking if I2C
was built-in, never if it was built as a module. This patch checks for either
since building both this driver and I2C as modules is possible.
Signed-off-by: NDaniel M. Weeks <dan@danweeks.net>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mcp23s08.c

@@ -77,7 +77,7 @@ struct mcp23s08_driver_data {
 
 /*----------------------------------------------------------------------*/
 
-#ifdef CONFIG_I2C
+#if IS_ENABLED(CONFIG_I2C)
 
 static int mcp23008_read(struct mcp23s08 *mcp, unsigned reg)
 {
@@ -399,7 +399,7 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 		break;
 #endif /* CONFIG_SPI_MASTER */
 
-#ifdef CONFIG_I2C
+#if IS_ENABLED(CONFIG_I2C)
 	case MCP_TYPE_008:
 		mcp->ops = &mcp23008_ops;
 		mcp->chip.ngpio = 8;
@@ -473,7 +473,7 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 
 /*----------------------------------------------------------------------*/
 
-#ifdef CONFIG_I2C
+#if IS_ENABLED(CONFIG_I2C)
 
 static int __devinit mcp230xx_probe(struct i2c_client *client,
 				    const struct i2c_device_id *id)