vboxvideo: Fix incorrect type in assignment sparse warning

Sparse emitted the following warning:
../drivers/staging/vboxvideo/vbox_fb.c:173:27: warning: incorrect type in assignment (different address spaces)
../drivers/staging/vboxvideo/vbox_fb.c:173:27:    expected char [noderef] <asn:2>*screen_base
../drivers/staging/vboxvideo/vbox_fb.c:173:27:    got void *virtual

The vbox_bo buffer object kernel mapping is handled by a call
to ttm_bo_kmap() prior to the assignment of bo->kmap.virtual to
info->screen_base of type char __iomem*.
Casting bo->kmap.virtual to char __iomem* in this assignment fixes
the warning.

vboxvideo: Fix address space of expression removal sparse warning

Sparse emitted the following warning:
../drivers/staging/vboxvideo/vbox_main.c:64:25: warning: cast removes address space of expression

vbox->vbva_buffers iomapping is handled by calling vbox_accel_init()
from vbox_hw_init().
__force attribute is used in assignment to vbva to fix the warning.
Signed-off-by: Alexander Kapshuk <alexander.kapshuk@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vboxvideo/vbox_fb.c

@@ -170,7 +170,7 @@ static int vboxfb_create(struct drm_fb_helper *helper,
 	drm_fb_helper_fill_var(info, &fbdev->helper, sizes->fb_width,
 			       sizes->fb_height);
 
-	info->screen_base = bo->kmap.virtual;
+	info->screen_base = (char __iomem *)bo->kmap.virtual;
 	info->screen_size = size;
 
 #ifdef CONFIG_DRM_KMS_FB_HELPER

drivers/staging/vboxvideo/vbox_main.c

@@ -61,7 +61,7 @@ void vbox_enable_accel(struct vbox_private *vbox)
 		if (vbox->vbva_info[i].vbva)
 			continue;
 
-		vbva = (void *)vbox->vbva_buffers + i * VBVA_MIN_BUFFER_SIZE;
+		vbva = (void __force *)vbox->vbva_buffers + i * VBVA_MIN_BUFFER_SIZE;
 		if (!vbva_enable(&vbox->vbva_info[i],
 				 vbox->guest_pool, vbva, i)) {
 			/* very old host or driver error. */