tdb: fix compilation with TDB_TRACE=1

tdb: fix compilation with TDB_TRACE=1

../../lib/tdb/common/tdb.c: In function ‘tdb_trace_record’:
../../lib/tdb/common/tdb.c:1224:22: error: ‘snprintf’ output truncated before the last format character [-Werror=format-truncation=]
 1224 |                 p += snprintf(p, 2, %02x, rec.dptr[i]);
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../lib/tdb/common/tdb.c:1224:22: note: ‘snprintf’ output 3 bytes into a destination of size 2
cc1: all warnings being treated as errors

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>