The size of our format string is known at compile time, and vfc_name has
a similarly fixed size. asprintf() can theoretically fail and leave us
with no description, but there's really no need: the vfs type name is
small enough that the resulting stack requirement is fairly small in the
grand scheme of things (we won't even exceed 64-bytes) and it's unlikely
to increase dramatically (if at all).
This technically leaves us oversized because both sizeof() results will
include a NUL terminator, but it seems better to err on the side of
caution.