i2c: Not all adapters have a parent

The code in acpi_i2c_register_devices() assumes that all i2c adapters
have a parent. This is not necessarily the case, for example the
i2c-stub driver instantiate a virtual i2c adapter without a parent.
Check for this to avoid a NULL pointer deference.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core.c

@@ -1134,6 +1134,9 @@ static void acpi_i2c_register_devices(struct i2c_adapter *adap)
 	acpi_handle handle;
 	acpi_status status;
 
+	if (!adap->dev.parent)
+		return;
+
 	handle = ACPI_HANDLE(adap->dev.parent);
 	if (!handle)
 		return;