SPML/UCX: Fix compilation warnings with GCC

[dmitrygx]

This patch fixes the following compilation warning produced by GCC 4.8.5:

make[2]: Entering directory `/root/ompi/oshmem/mca/spml/ucx'
  CC       spml_ucx_component.lo
  CC       spml_ucx.lo
spml_ucx.c: In function 'mca_spml_ucx_del_procs':
spml_ucx.c:134:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (w = 0; w < ucp_workers; w++) {
                       ^
spml_ucx.c: In function 'mca_spml_ucx_add_procs':
spml_ucx.c:328:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (w = 0; w < ucp_workers; w++) {
                   ^
spml_ucx.c:335:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (w = 0; w < ucp_workers; w++, i++) {
                       ^
spml_ucx.c:389:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (w = 0; w < ucp_workers; w++) {
                       ^
spml_ucx.c:284:18: warning: unused variable 'k' [-Wunused-variable]
     size_t i, j, k, w, n;
                  ^
spml_ucx.c: In function 'mca_spml_ucx_ctx_create':
spml_ucx.c:754:31: warning: unused variable 'active_array' [-Wunused-variable]
     mca_spml_ucx_ctx_array_t *active_array = &mca_spml_ucx.active_array;
                               ^
  CCLD     mca_spml_ucx.la

[dmitrygx]

@brminich @hoopoepg @janjust could you review pls?

[artemry-nv]

@dmitrygx
Wrong commit author - Mellanox CI failed.

[dmitrygx]

@dmitrygx
Wrong commit author - Mellanox CI failed.

@artemry-mlnx thank you, fixed!

[dmitrygx]

@brminich could you check the fix for your comment pls?

[dmitrygx]

@yosefe could you review, please?