ARM: dts: Fix NAND last partition size on LDP

Fix the following warning during the boot:

mtd: partition "Filesystem" extends beyond the end of device
"omap2-nand.0" -- size truncated to 0x6000000

Looks like I got the last partition size wrong while setting
up the .dts file. Note that this does not affect the partition
as the size has been getting truncated to the right size.

Signed-off-by: Tony Lindgren <tony@atomide.com>