mtd: nand: fsl_ifc: Fix nand waitfunc return value

mtd: nand: fsl_ifc: Fix nand waitfunc return value

As per the IFC hardware manual, Most significant 2 bytes in
nand_fsr register are the outcome of NAND READ STATUS command.

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

Fixes: 82771882d960 ("NAND Machine support for Integrated Flash Controller")
Cc: [email protected] # v3.18+
Signed-off-by: Jagdish Gediya <[email protected]>
Reviewed-by: Prabhakar Kushwaha <[email protected]>
Signed-off-by: Boris Brezillon <[email protected]>