Fix argument list for ber_set_writecallback

OK claudio@

src/lib/libutil/ber_set_header.3

@@ -1,4 +1,4 @@
-.\" $OpenBSD: ber_set_header.3,v 1.2 2019/05/21 12:30:07 rob Exp $
+.\" $OpenBSD: ber_set_header.3,v 1.3 2019/08/14 19:08:03 martijn Exp $
 .\"
 .\" Copyright (c) 2007, 2012 Reyk Floeter <reyk@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: May 21 2019 $
+.Dd $Mdocdate: August 14 2019 $
 .Dt BER_SET_HEADER 3
 .Os
 .Sh NAME
@@ -36,7 +36,9 @@
 .Fn "ber_calc_len" "struct ber_element *root"
 .Ft "void"
 .Fo "ber_set_writecallback"
-.Fa "void (*cb)(void *arg, sizeof_t offs)"
+.Fa "struct ber_element *elm"
+.Fa "void (*cb)(void *arg, size_t offs)"
+.Fa "void *arg"
 .Fc
 .Ft "void"
 .Fn "ber_link_elements" "struct ber_element *prev" "struct ber_element *elm"