firmware/sysfb: fix an error code in sysfb_init()

This error path accidentally returns success when it should preserve the
error code from sysfb_parent_dev().

Fixes: 4e754597 ("firmware/sysfb: Create firmware device only for enabled PCI devices")
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/aaaa2e13-849b-41a0-8186-25f3d2a16f86@moroto.mountain