drm/msm: Use struct fb_info.screen_buffer

The fbdev framebuffer is in system memory. Store the address in
the field 'screen_buffer'. Fixes the following sparse warning.

../drivers/gpu/drm/msm/msm_fbdev.c:124:26: warning: incorrect type in assignment (different address spaces)
../drivers/gpu/drm/msm/msm_fbdev.c:124:26: expected char [noderef] __iomem *screen_base
../drivers/gpu/drm/msm/msm_fbdev.c:124:26: got void *

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/538531/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/msm/msm_fbdev.c

···
 
 	drm_fb_helper_fill_info(fbi, helper, sizes);
 
-	fbi->screen_base = msm_gem_get_vaddr(bo);
-	if (IS_ERR(fbi->screen_base)) {
-		ret = PTR_ERR(fbi->screen_base);
+	fbi->screen_buffer = msm_gem_get_vaddr(bo);
+	if (IS_ERR(fbi->screen_buffer)) {
+		ret = PTR_ERR(fbi->screen_buffer);
 		goto fail;
 	}
 	fbi->screen_size = bo->size;