drm/radeon: replace min/max nesting with clamp()

The clamp() macro explicitly expresses the intent of constraining
a value within bounds.Therefore, replacing min(max(a, b), c) and
max(min(a,b),c) with clamp(val, lo, hi) can improve code readability.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Xichao Zhao <zhao.xichao@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>