clk: sunxi-ng: nkm: Use correct parameter name for parent HW

ccu_nkm_round_rate() takes a clk_hw as parameter "hw". Since "hw" is the
nkm clock's parent clk_hw, not the clk_hw of the nkm clock itself,
change the parameter name to "parent_hw" to make it more clear what
we're dealing with.

Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Link: https://lore.kernel.org/r/20230807-pll-mipi_set_rate_parent-v6-1-f173239a4b59@oltmanns.dev
Signed-off-by: Chen-Yu Tsai <wens@csie.org>