Add the missing space between .asciz directive and opening quote for some
lines within #ifdef BTXLDR_VERBOSE/#endif

Reported by: Kevin Zheng <kzheng@juniper.net>
Reviewed by: jhb
Approved by: sjg (mentor)
Obtained from: Juniper Networks, Inc.
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D7464