stand/lua: Chop off the decimal for numbers passed to setcursor

Decimals screw up the escape sequence and the cursor will not get set. Right
now this only affects setting the cursor for drawing "Welcome to FreeBSD" --
the resulting number after our (x+(w/2)-9) calculation gets output as
"14.0."

This should be fixed at the interpreter level, rather than here, but this is
not a widespread problem at the moment so we'll fix it up in further work.

Reported by: David Wolfskill <david@catwhisker.org>
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D14375