[ARM] 4399/2: S3C2443: Fix SMDK2443 nand timings

Reduce the Twrph0 timing slightly to fit on an SMDK2443. This
should still produce valid timings for the NAND devices as it
is still over the smallest device fitted to these boards.

Signed-off-by: Ben Dooks <(address hidden)>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>