drm/amd/amdgpu: fix refcount leak

stable inclusion
from stable-v4.19.193
commit 599e5d61ace952b0bb9bd942b198bbd0cfded1d7
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9BGUR
CVE: CVE-2021-47144

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=599e5d61ace952b0bb9bd942b198bbd0cfded1d7



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[ Upstream commit fa7e6abc ]

[Why]
the gem object rfb->base.obj[0] is get according to num_planes
in amdgpufb_create, but is not put according to num_planes

[How]
put rfb->base.obj[0] in amdgpu_fbdev_destroy according to num_planes

Signed-off-by: Jingwen Chen <Jingwen.Chen2@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Liu Mingrui <liumingrui@huawei.com>