oxnas: also reset GPIO B registers on boot

Clear both, SYS_CTRL_*_SEL and SEC_CTRL_*_SEL on boot instead of
writing to SYS_CTRL_*_SEL twice which looks like a copy-paste error.
Thanks to anonymous to bring this up in #21892!

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

SVN-Revision: 49042