drm/amd: use clamp() in amdgpu_pll_get_fb_ref_div()

When it needs to get a value within a certain interval, using clamp()
makes the code easier to understand than min(max()).

Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Li Zetao <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c

···
 		ref_div_max = min(128 / post_div, ref_div_max);
 
 	/* get matching reference and feedback divider */
-	*ref_div = min(max(DIV_ROUND_CLOSEST(den, post_div), 1u), ref_div_max);
+	*ref_div = clamp(DIV_ROUND_CLOSEST(den, post_div), 1u, ref_div_max);
 	*fb_div = DIV_ROUND_CLOSEST(nom * *ref_div * post_div, den);
 
 	/* limit fb divider to its maximum */