[PATCH] nand_wait() timeout fixes

Two fixes for the nand_wait() function in
drivers/nand/nand_base.c:

1. Use correct timeouts. The original timeouts in Linux
source are 400ms and 20ms not 40s and 20s

2. Return correct error value in case of timeout. 0 is
interpreted as OK.

Signed-off-by: Rui Sousa <rui.sousa@laposte.net>
Signed-off-by: Stefan Roese <sr@denx.de>