[ARM] omap: move propagate_rate() calls into generic omap clock code

propagate_rate() is recursive, so it makes sense to minimise the
amount of stack which is used for each recursion.  So, rather than
recursing back into it from the ->recalc functions if RATE_PROPAGATES
is set, do that test at the higher level.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>