[PATCH] fix system clock on ruffian

[PATCH] fix system clock on ruffian

Unlike most other alphas, ruffian uses i8253 timer instead of RTC
as the system clock source. However, the PIT clock divisor (LATCH)
is bogus since CLOCK_TICK_RATE has been changed to 32 KHz.
Fixed using recently introduced PIT_TICK_RATE macro.

Ivan.