omap2 clock: drop meaningless RATE_CKCTLs

Drop the RATE_CKCTL clock flag from iva1_mpu_int_ifck, gfx_ick, ssi_l4_ick,
and dss_ick.  These clocks are not source-selectable, which is the practical
meaning of RATE_CKCTL in the 2420 clock framework.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>