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.

This bug introduced in v3.14-rc1 breaks various devices on the Lager and
Kolesh shmobile boards and should thus be considered as a regression for
which a fix during the -rc series is appropriate.

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