pruss hwmod RSTST register wrongly points to PWRSTCTRL register in case of
am43xx. Fix the RSTST register offset value.

This can lead to setting of wrong power state values for PER domain.

Fixes: 1c7e224d ("ARM: OMAP2+: hwmod: AM335x: runtime register update")
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>