mtd: nand: fsl_ifc: Fix nand waitfunc return value

As per the IFC hardware manual, Most significant byte in nand_fsr
register is the outcome of NAND READ STATUS command.

So status value need to be shifted as per the nand framework
requirement.

Signed-off-by: Jagdish Gediya <jagdish.gediya@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>