drm/amdgpu: fix vram reservation issue

drm/amdgpu: fix vram reservation issue

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: c9cad937c0c5 ("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 d38eaf27de1b8584f42d6fb3f717b7ec44b3a7a1)