bsdinstall: fix ps3 regression

b6644f5 introduces FREEBSD_BOOTLABEL="FreeBSD" as default value
but cc42ef5 removed this line, expecting it to be set by update_uefi_bootentry()

But ps3 don't use this function so its broken completely.

So we add this line back.

Signed-off-by: Chattrapat Sangmanee <aomsin27@hotmail.co.th>
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1594