drm/amdgpu/gfx: refine fw hdr check fuction

The return value of function amdgpu_ucode_hdr_version
doesn't make sense, so change it to return true when
fw header version is match with passed in parameters.

Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>