drivers: gpu: Mark function as static in qxl_kms.c

Mark function qxl_device_init() as static in drm/qxl/qxl_kms.c because
it is not used outside this file.

This eliminates the following warning in drm/qxl/qxl_kms.c:
drivers/gpu/drm/qxl/qxl_kms.c:118:5: warning: no previous prototype for ‘qxl_device_init’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/qxl/qxl_kms.c

···
 	qxl_garbage_collect(qdev);
 }
 
-int qxl_device_init(struct qxl_device *qdev,
+static int qxl_device_init(struct qxl_device *qdev,
 		    struct drm_device *ddev,
 		    struct pci_dev *pdev,
 		    unsigned long flags)