share: man: fix coredumper_register(9)'s init_fn

A last-minute change tweaked the prototype because we can just fetch
the compression format from the compressor, but I missed updating the
manpage to match it.

Fixes:	ce51f79913 ("kern: abstract away the vnode coredumper [..]")

share/man/man9/coredumper_register.9

@@ -31,8 +31,8 @@ struct coredumper {
 .Ed
 .Pp
 .Ft int
-.Fn coredump_init_fn "const struct coredump_writer *" "const struct coredump_params *"
-"int"
+.Fn coredump_init_fn "const struct coredump_writer *" \
+"const struct coredump_params *"
 .Ft int
 .Fn coredump_write_fn "const struct coredump_writer *" "const void *" "size_t" \
 "off_t" "enum uio_seg" "struct ucred *" "size_t *" "struct thread *"