svga: Ensure that the wrong vdecls don't get used in swtnl path

svga: Ensure that the wrong vdecls don't get used in swtnl path

The draw module set new state that didn't require swtnl which caused need_swtnl to
be unset. This caused the call from to svga_update_state(svga, SVGA_STATE_SWTNL_DRAW)
from the vbuf backend to overwrite the vdecls we setup there to be overwritten with
the real buffers vdecls.