drm/amdgpu: Call drm_framebuffer_init last for framebuffer init

drm/amdgpu: Call drm_framebuffer_init last for framebuffer init

Once drm_framebuffer_init has returned 0, the framebuffer is hooked up
to the reference counting machinery and can no longer be destroyed with
a simple kfree. Therefore, it must be called last.

If drm_framebuffer_init returns 0 but its caller then returns non-0,
there will likely be memory corruption fireworks down the road.
The following lead me to this fix:

[   12.891228] kernel BUG at lib/list_debug.c:25!
[...]
[   12.891263] RIP: 0010:__list_add_valid+0x4b/0x70
[...]
[   12.891324] Call Trace:
[   12.891330]  drm_framebuffer_init+0xb5/0x100 [drm]
[   12.891378]  amdgpu_display_gem_fb_verify_and_init+0x47/0x120 [amdgpu]
[   12.891592]  ? amdgpu_display_user_framebuffer_create+0x10d/0x1f0 [amdgpu]
[   12.891794]  amdgpu_display_user_framebuffer_create+0x126/0x1f0 [amdgpu]
[   12.891995]  drm_internal_framebuffer_create+0x378/0x3f0 [drm]
[   12.892036]  ? drm_internal_framebuffer_create+0x3f0/0x3f0 [drm]
[   12.892075]  drm_mode_addfb2+0x34/0xd0 [drm]
[   12.892115]  ? drm_internal_framebuffer_create+0x3f0/0x3f0 [drm]
[   12.892153]  drm_ioctl_kernel+0xe2/0x150 [drm]
[   12.892193]  drm_ioctl+0x3da/0x460 [drm]
[   12.892232]  ? drm_internal_framebuffer_create+0x3f0/0x3f0 [drm]
[   12.892274]  amdgpu_drm_ioctl+0x43/0x80 [amdgpu]
[   12.892475]  __se_sys_ioctl+0x72/0xc0
[   12.892483]  do_syscall_64+0x33/0x40
[   12.892491]  entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: a4a16271059cd1 "drm/amdgpu: Verify bo size can fit framebuffer size on init."
Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>