Input: synaptics_i2c - wrap suspend and resume in CONFIG_PM_SLEEP

CONFIG_PM is defined when CONFIG_PM_SLEEP or CONFIG_PM_RUNTIME is defined,
however suspend and resume methods are only valid in context of
CONFIG_PM_SLEEP. If only CONFIG_PM_RUNTIME is defined we get the following
warning (courtesy of Geerts randconfig builds):

	synaptics_i2c.c: warning: 'synaptics_i2c_resume' defined but not used
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/mouse/synaptics_i2c.c

@@ -619,7 +619,7 @@ static int __devexit synaptics_i2c_remove(struct i2c_client *client)
 	return 0;
 }
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 static int synaptics_i2c_suspend(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);