xf86platformBus: Add assertion to avoid (fatal) compiler warning

Compilation of -video-intel started failing in gnome-continuous,
it's because xserver has -Werror=return-type on, and gcc can't
prove this function always returns a value:

   /usr/include/xorg/xf86platformBus.h:119:1: error: control reaches end of non-void function [-Werror=return-type]

Let's add assertions to the accessor functions to fix this.

Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

hw/xfree86/common/xf86platformBus.h

@@ -115,6 +115,9 @@ _xf86_get_platform_device_attrib(struct xf86_platform_device *device, int attrib
         return xf86_platform_device_odev_attributes(device)->busid;
     case ODEV_ATTRIB_DRIVER:
         return xf86_platform_device_odev_attributes(device)->driver;
+    default:
+        assert(FALSE);
+        return NULL;
     }
 }
 
@@ -135,6 +138,9 @@ _xf86_get_platform_device_int_attrib(struct xf86_platform_device *device, int at
         return xf86_platform_device_odev_attributes(device)->major;
     case ODEV_ATTRIB_MINOR:
         return xf86_platform_device_odev_attributes(device)->minor;
+    default:
+        assert(FALSE);
+        return 0;
     }
 }