platform/x86: apple-gmux: fix gmux_get_client_id()'s return type

The method struct vga_switcheroo_handler::get_client_id() is defined
as returning an 'enum vga_switcheroo_client_id' but the implementation
in this driver, gmux_get_client_id(), returns an 'int'.

Fix this by returning 'enum vga_switcheroo_client_id' in this driver too.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/apple-gmux.c

@@ -495,7 +495,7 @@ static int gmux_set_power_state(enum vga_switcheroo_client_id id,
 	return gmux_set_discrete_state(apple_gmux_data, state);
 }
 
-static int gmux_get_client_id(struct pci_dev *pdev)
+static enum vga_switcheroo_client_id gmux_get_client_id(struct pci_dev *pdev)
 {
 	/*
 	 * Early Macbook Pros with switchable graphics use nvidia