usnic: minor updates from code review

Three minor updates from the code review of
#933:

* Remove an extra blank line a show_help message
* We no longer allow -1 for the MCA param btl_usnic_av_eq_num, so
  change the flag to REGINT_GE_ONE
* Change "num_blocks" definition to be in terms of block_len (not
  eq_size)

(cherry picked from commit open-mpi/ompi@9f3ed00)

Author: jsquyres

opal/mca/btl/usnic/btl_usnic_mca.c

@@ -237,7 +237,7 @@ int opal_btl_usnic_component_register(void)
     mca_btl_usnic_component.cq_num = (int32_t) cq_num;
 
     CHECK(reg_int("av_eq_num", "Number of event queue entries for peer address resolution",
-                  1024, &av_eq_num, REGINT_NEG_ONE_OK, OPAL_INFO_LVL_5));
+                  1024, &av_eq_num, REGINT_GE_ONE, OPAL_INFO_LVL_5));
     mca_btl_usnic_component.av_eq_num = (int32_t) av_eq_num;
 
     CHECK(reg_int("base_udp_port", "Base UDP port to use for usNIC communications.  If 0, system will pick the port number.  If non-zero, it will be added to each process' local rank to obtain the final port number (default: 0)",

opal/mca/btl/usnic/btl_usnic_module.c

@@ -411,7 +411,7 @@ static int add_procs_create_endpoints(struct opal_btl_usnic_module_t* module,
     size_t eq_size = module->av_eq_size - 8;
     size_t block_len = eq_size;
     size_t num_av_inserts = nprocs * USNIC_NUM_CHANNELS;
-    size_t num_blocks = num_av_inserts / eq_size;
+    size_t num_blocks = num_av_inserts / block_len;
     if (eq_size % num_av_inserts != 0) {
         ++num_blocks;
     }

opal/mca/btl/usnic/help-mpi-btl-usnic.txt

@@ -241,7 +241,6 @@ abort.
   Current ARP timeout: %d (btl_usnic_arp_timeout MCA param)
 #
 [fi_av_eq too small]
-
 The usnic BTL was told to create an address resolution queue that was
 too small via the mca_btl_usnic_av_eq_num MCA parameter.  This
 parameter controls how many outstanding peer address resolutions can