plugin/ssa_comparison.c: Bug fix in ssa_db_link_cmp

Wrong pointer was re-initialized in ssa_db_link_cmp()
method (p_tbl_rec_old was initialized twice instead
of p_tbl_rec_new).

The bug was found by Lenny's verification system:

==2404== Invalid read of size 2
==2404==    at 0x16899B9C: ssa_db_link_cmp (ssa_comparison.c:510)
==2404==    by 0x16899DA4: ssa_db_diff_table_cmp (ssa_comparison.c:571)
==2404==    by 0x1689A5C1: ssa_db_diff_compare_subnet_tables (ssa_comparison.c:779)
==2404==    by 0x1689B0B8: ssa_db_compare (ssa_comparison.c:1376)
==2404==    by 0x168889E0: core_extract_handler (core.c:778)
==2404==    by 0x3102207850: start_thread (in /lib64/libpthread-2.12.so)
==2404==    by 0x178CA6FF: ???
==2404==  Address 0x19bbfea8 is not stack'd, malloc'd or (recently) free'd

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>