drm/radeon: Remove test for !screen_base in fbdev probing

The screen_base field comes from the fbdev BO and contains the fbdev
framebuffer base address. We get the BO memory via radeon_bo_kmap(),
which already reports the error -ENOMEM if the buffer could not be
mapped. So remove the later test for screen_base, which will never
be NULL at this point.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_fb.c

@@ -247,11 +247,6 @@ static int radeonfb_create(struct drm_fb_helper *helper,
 
 	/* Use default scratch pixmap (info->pixmap.flags = FB_PIXMAP_SYSTEM) */
 
-	if (info->screen_base == NULL) {
-		ret = -ENOSPC;
-		goto out;
-	}
-
 	DRM_INFO("fb mappable at 0x%lX\n",  info->fix.smem_start);
 	DRM_INFO("vram apper at 0x%lX\n",  (unsigned long)rdev->mc.aper_base);
 	DRM_INFO("size %lu\n", (unsigned long)radeon_bo_size(rbo));