drm/amdgpu: fix wrong executable setting for dimgrey_cavefish_reg_init.c

Remove executable configuration for the file.

Reported-by: Ming Wang <wangming01@loongson.cn>
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>