ddr: altera: Fix DRAM end value in protection rule

The hi address bitfield in the protection rule must be set to
the last address in the region which the rule represents. The
behavior is now in-line with code generated by Quartus 15.1 .

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Chin Liang See <clsee@altera.com>