soc: ti: omap-prm: Do not check rstst bit on deassert if already deasserted

If a rstctrl reset bit is already deasserted, we can just bail out early
not wait for rstst to clear. Otherwise we can have deassert fail for
already deasserted resets.

Fixes: c5117a78

 ("soc: ti: omap-prm: poll for reset complete during de-assert")
Signed-off-by: Tony Lindgren <tony@atomide.com>