ARM: OMAP4+: Have _omap4_wait_target_* check for valid clkctrl_offs

Previously the low-level CM call internal to the
_omap4_wait_target_ready/disable calls was responsible for checking for
a valid clkctrl_offs. Now we must also consider the value of the
prcm.omap4.flags because if HWMOD_OMAP4_ZERO_CLKCTRL_OFFSET is set in
the flags then clkctrl_offs of 0 is valid.

Let's add this check into the _omap4_wait_target_ready/disable where we
have access to both the clkctrl_offs and the flags values and simply
return 0 without calling the low level CM call at all, which would have
returned 0 anyway if the clktrl_offs was zero.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>