clk: renesas: rcar-gen3: Update Z clock rate formula in comments

The fixed divider in the calculation of the Z and Z2 clock rates was
generalized from a hardcoded value of two to a parameterized value, but
the comments were not updated accordingly.

Fixes: 20cc05ba ("clk: renesas: rcar-gen3: Parameterise Z and Z2 clock fixed divisor")
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>
Link: https://lore.kernel.org/r/20210326120100.1577596-2-geert+renesas@glider.be

drivers/clk/renesas/rcar-gen3-cpg.c

@@ -38,7 +38,8 @@
  * Traits of this clock:
  * prepare - clk_prepare only ensures that parents are prepared
  * enable - clk_enable only ensures that parents are enabled
- * rate - rate is adjustable.  clk->rate = (parent->rate * mult / 32 ) / 2
+ * rate - rate is adjustable.
+ *        clk->rate = (parent->rate * mult / 32 ) / fixed_div
  * parent - fixed parent.  No clk_set_parent support
  */
 #define CPG_FRQCRB			0x00000004