rtld: fix display of the mapbase for the traced objects

Commit 24d0c9c1f565bab6e introduced the following regression:
% ldd /bin/ls
/bin/ls:

libutil.so.9 => /lib/libutil.so.9 (0x1021000)
libncursesw.so.9 => /lib/libncursesw.so.9 (0x1021000)
libc.so.7 => /lib/libc.so.7 (0x1021000)

Note that the base address is the same for all displayed libraries.

Fix it by passing correct object to trace_print_obj().

Fixes: 24d0c9c1f565bab6e
Reviewed by: jrtc27
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Differential revision: https://reviews.freebsd.org/D36198