[ARM] 3617/1: ep93xx: fix slightly incorrect timer tick rate

Patch from Lennert Buytenhek

The tick rate of timers 1-3 isn't exactly 508 kHz as some parts of the
relevant documentation claim, but more like 508.469 kHz (14.7456 MHz
divided by 29.)

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>