mtd: brcmnand: Fix v7.1 register offsets

The BRCMNAND controller revision 7.1 is almost 100% compatible with the
previous v6.0 register offset layout, except for the Correctable Error
Reporting Threshold registers. Fix this by adding another table with the
correct offsets for CORR_THRESHOLD and CORR_THRESHOLD_EXT.

Fixes: 27c5b17c ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>