mpc8313erdb: fix mtdparts address

Fix a copy-and-paste error when adapting mpc8315erdb mtdparts
to mpc8313erdb.  mtdids was already using the proper address
on mpc8313erdb.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>