drm/amd/display: fix documentation for amdgpu_dm_verify_lut3d_size()

It takes the plane state rather than the crtc state.

Fixes: aba8b76b ("drm/amd/display: add plane shaper LUT support")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Melissa Wen <mwen@igalia.com>
Cc: Harry.Wentland@amd.com