[ARM] omap: fix clock reparenting in omap2_clk_set_parent()

When changing the parent of a clock, it is necessary to keep the
clock use counts balanced otherwise things the parent state will
get corrupted.  Since we already disable and re-enable the clock,
we might as well use the recursive versions instead.

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