kbdcontrol: correct bell frequency for vt(4)

Do the 1193182 / pitch hack only for sc(4).

PR: 281713
Reported by: Rudolf Polzer
Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D46803

(cherry picked from commit f65c19a242de322930f6a1cd7d5e6bf3ce19ce42)