OMAP clock: drop RATE_FIXED clock flag

The RATE_FIXED clock flag is pointless.  In the OMAP1 clock code, it
simply causes the omap1_clk_round_rate() function to return the
current rate of the clock.  omap1_clk_round_rate(), however, should
never be called for a fixed-rate clock, since none of these clocks
have a .round_rate function pointer set in their struct clk records.
Similarly, in the OMAP2+ clock code, the RATE_FIXED flag just causes
the clock code to emit a warning if the OMAP clock maintainer was
foolish enough to add a .round_rate function pointer to a fixed-rate
clock.  "Doctor, it hurts when I pretend that a fixed-rate clock is
rate-changeable."  "Then don't pretend that a fixed-rate clock is
rate-changeable."  It has no functional value.  This patch drops the
RATE_FIXED clock flag, removing it from all clocks that are so marked.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>