argconfig: fix possible buffer overrun
argconfig: fix possible buffer overrun

Newer compilers will detect this bug and report:

  cli/argconfig.c: In function ‘argconfig_parse_comma_range’:
  cli/argconfig.c:1111:2: warning: ‘strcpy’ writing one too many bytes
     into a region of a size that depends on ‘strlen’ [-Wstringop-overflow=]
         1111 |  strcpy(buf, str);
	      |  ^~~~~~~~~~~~~~~~
  cli/argconfig.c:1105:7: note: at offset 0 to an object declared here
         1105 |  char buf[strlen(str)];
              |       ^~~

This is easily fixed by adding one to the size of buf.

Microsemi/switchtec-user,Microsemi/switchtec-user