drm/aspeed: Call drm_fbdev_generic_setup after drm_dev_register

drm/aspeed: Call drm_fbdev_generic_setup after drm_dev_register

The following backtrace is seen when running aspeed G5 kernels.

WARNING: CPU: 0 PID: 1 at drivers/gpu/drm/drm_fb_helper.c:2233 drm_fbdev_generic_setup+0x138/0x198
aspeed_gfx 1e6e6000.display: Device has not been registered.
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3 #1
Hardware name: Generic DT based system
Backtrace:
[<8010d6d0>] (dump_backtrace) from [<8010d9b8>] (show_stack+0x20/0x24)
r7:00000009 r6:60000153 r5:00000000 r4:8119fa94
[<8010d998>] (show_stack) from [<80b8cb98>] (dump_stack+0xcc/0xec)
[<80b8cacc>] (dump_stack) from [<80123ef0>] (__warn+0xd8/0xfc)
r7:00000009 r6:80e62ed0 r5:00000000 r4:974c3ccc
[<80123e18>] (__warn) from [<80123f98>] (warn_slowpath_fmt+0x84/0xc4)
r9:00000009 r8:806a0140 r7:000008b9 r6:80e62ed0 r5:80e631f8 r4:974c2000
[<80123f18>] (warn_slowpath_fmt) from [<806a0140>] (drm_fbdev_generic_setup+0x138/0x198)
r9:00000001 r8:9758fc10 r7:9758fc00 r6:00000000 r5:00000020 r4:9768a000
[<806a0008>] (drm_fbdev_generic_setup) from [<806d4558>] (aspeed_gfx_probe+0x204/0x32c)
r7:9758fc00 r6:00000000 r5:00000000 r4:9768a000
[<806d4354>] (aspeed_gfx_probe) from [<806dfca0>] (platform_drv_probe+0x58/0xa8)

Since commit 1aed9509b29a6 ("drm/fb-helper: Remove return value from
drm_fbdev_generic_setup()"), drm_fbdev_generic_setup() must be called
after drm_dev_register() to avoid the warning. Do that.

Fixes: 1aed9509b29a6 ("drm/fb-helper: Remove return value from drm_fbdev_generic_setup()")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200701001002.74997-1-linux@roeck-us.net