clk: renesas: rcar-gen3: Make cpg_z_clk.mask u32

cpg_z_clk.mask contains a mask for a 32-bit register.
Hence its size can be reduced from unsigned long to u32.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20210326120100.1577596-3-geert+renesas@glider.be