In commit c59b537 (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.