ipq806x: nand: Add missing writebufsize initialization for ubi fastmap

The writebufsize is introduced in mtd struct for the ubi fastmap
support.
This is not initialized in the qpic nand driver which leads to ubi
error.
Fixed the following ubi error.
	bad write buffer size 0 for 2048 min. I/O unit
	UBI init error 22

Change-Id: I35778366b95930bd01108bf300f073ee21940bc6
Signed-off-by: Ajay Kishore <akisho@codeaurora.org>
1 file changed