soc: renesas: rmobile-sysc: Fix some leaks in rmobile_init_pm_domains()

This code needs to call iounmap() on one error path.

Fixes: 2173fc7c ("ARM: shmobile: R-Mobile: Add DT support for PM domains")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20200923113142.GC1473821@mwanda


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>