drm/amdgpu: fix vram reservation issue

[ Upstream commit 10ef476a ]

The vram block allocation flag must be cleared
before making vram reservation, otherwise reserving
addresses within the currently freed memory range
will always fail.

Fixes: c9cad937 ("drm/amdgpu: add drm buddy support to amdgpu")
Signed-off-by: YiPeng Chai <YiPeng.Chai@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d38eaf27)
Signed-off-by: Sasha Levin <sashal@kernel.org>