clk: shmobile: rcar-gen2: Fix qspi divisor

The qspi clock divisor is incorrectly set to twice the value it should
have, possibly because it has been computed based on PLL1 as the clock
parent instead of PLL1 / 2 (the datasheets specifies the qspi nominal
frequencies, not the divisor values). Fix it.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Mike Turquette <mturquette@linaro.org>