hw/nand.c: Fix nand erase operation

hw/nand.c: Fix nand erase operation

Usually, nand erase operation has only 2 or 3 address cycles.
We need to mask s->addr to zero unset stale high-order bytes in the nand address
before using it as the erase address.

This fixes the NAND erase operation in Linux.

[PC: Generalised to work for any number of address cycles rather than just 3]

Signed-off-by: Wendy Liang <jliang@xilinx.com>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 1364967188-26711-1-git-send-email-peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>