ARM: OMAP: dts: N950/N9: fix onenand timings

Commit a758f50f ("mtd: onenand: omap2: Configure driver from DT")
started using DT specified timings for GPMC, and as a result the
OneNAND stopped working on N950/N9 as we had wrong values in the DT.
Fix by updating the values to bootloader timings that have been tested
to be working on both Nokia N950 and N9.

Fixes: a758f50f

 ("mtd: onenand: omap2: Configure driver from DT")
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>