drm/amdgpu: initialize amdgpu_cgs_acpi_eval_object result value

amdgpu_cgs_acpi_eval_object() returned the value of variable "result"
without initializing it first.

This bug has been found by compiling the kernel with clang.  The
compiler complained:

    drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c:972:14: error: variable
    'result' is used uninitialized whenever 'for' loop exits because its
    condition is false [-Werror,-Wsometimes-uninitialized]
            for (i = 0; i < count; i++) {
                        ^~~~~~~~~
    drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c:1011:9: note: uninitialized
    use occurs here
            return result;
                   ^~~~~~
    drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c:972:14: note: remove the
    condition if it is always true
            for (i = 0; i < count; i++) {
                        ^~~~~~~~~
    drivers/gpu/drm/amd/amdgpu/amdgpu_cgs.c:864:12: note: initialize the
    variable 'result' to silence this warning
            int result;
                      ^
                       = 0

Fixes: 3f1d35a0

 ("drm/amdgpu: implement new cgs interface for acpi
function")
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>