Stop setting ri->ri_bs to prevent a panic caused by rasops accessing its

Stop setting ri->ri_bs to prevent a panic caused by rasops accessing its
uninitialized content.  When we rasops_init() with RI_VCONS, a new screen
is allocated.  If ri->ri_bs is set, this will be copied.  Otherwise a new
one will be allocated and filled with ASCII spaces.  Copying the ri->ri_bs
is useful in case we have an early console which contents we want to keep.
As we do not have an early console here, there's no point in setting it at
the moment.

With this my Hetzner arm64 VM doesn't panic anymore.

ok jcs@ kettenis@