nand_spl: nand_boot.c: Init nand_chip.options to 0

Patch 65a9db7b [nand_spl: Fix large page nand_command()] broke
nand booting on canyonlands. "options" has to be initialized to
0. If not, boards might have the NAND_BUSWIDTH_16 bit set,
resulting in wrong offset calculation.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Alex Waterman <awaterman@dawning.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>