ARM: OMAP2420: Cosmetic fix for timer clock aliases

In commit c59b537d (ARM: OMAP2+: Simplify dmtimer clock aliases) new clock
aliases were added for OMAP2+ devices. For OMAP2420, I incorrectly set the
clock flag as CK_243X instead of CK_242X. This did not introduce a regression
as the clock flags are not checked for OMAP2 devices. This also explains why
I did not catch this when testing on OMAP2420.

Fix the clock flags for these aliases for correctness.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>