drm/amd/display: Use kvfree() to free coeff in build_regamma()

Use kvfree() instead of kfree() to free coeff in build_regamma()
because the memory is allocated with kvzalloc().

Fixes: e752058b8671 ("drm/amd/display: Optimize gamma calculations")
Cc: [e-mail]
Signed-off-by: Denis Efremov <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/modules/color/color_gamma.c

···
 	pow_buffer_ptr = -1; // reset back to no optimize
 	ret = true;
 release:
-	kfree(coeff);
+	kvfree(coeff);
 	return ret;
 }