Platform Nand: Set the GPIO for NAND read as input

This patch is from Frank.Shew,fshew@geometrics.com to fix the
following problem:having extremely slow responses with the NAND
due to timeouts on the ready status signal, which eventually
caused the watchdog to time out.

Signed-off-by: Aaron Wu <Aaron.Wu@analog.com>
Signed-off-by: Steven Miao <realmz6@gmail.com>