[WATCHDOG] iTCO_wdt.c - fix ACPI Base register

The ACPI/PM base I/O address which is the base
for the TCO registers is defined as bits [15:7]
(highest bit is 31, lowest is 0)

The code however only reads bits [14:7]. So
        base_address &= 0x00007f80;
needs to be:
        base_address &= 0x0000ff80;

This patch fixes this.

Signed-off-by: Ate Wijma <ajwijma@hotmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>