The cast to uint8_t happens before the right shift so this always sets
.m3arb to zero.  The cast is actually a no-op so we can remove it.

Fixes: 3bace359 ('drm/amd/powerplay: add hardware manager sub-component')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>