OMAP2xxx: clock: remove dsp_irate_ick

After commit 81b34fbe ("OMAP2 clock:
split OMAP2420, OMAP2430 clock data into their own files"), it's
possible to remove dsp_irate_ick from the OMAP2420 and OMAP2430 clock
files.  It was originally only needed due to a 2420/2430 clock tree difference,
and now that the data is in separate files, it's superfluous.

Signed-off-by: Paul Walmsley <paul@pwsan.com>