[PATCH 14/14] fix type mismatch in parse_line()

When compiling with CC=clang the following warning is emitted

 tools.c:150:14: warning: expression which evaluates to zero treated as a null pointer constant of type 'char *' [-Wnon-literal-null-conversion]
	                        argv[j] = NULLCHAR;
	                                  ^~~~~~~~
 ./makedumpfile.h:224:18: note: expanded from macro 'NULLCHAR'
 #define NULLCHAR        ('\0')

As argv is initialized to NULL this line can simply be removed.

Signed-off-by: Philipp Rudo <prudo@redhat.com>