testsuite: Fix warnings

Updates #4662

testsuites/fstests/tftpfs/init.c

@@ -919,7 +919,7 @@ T_TEST_CASE( tftp_read_null_buffer )
  */
 T_TEST_CASE( tftp_write_null_tftp_handle )
 {
-  char data_buffer[10];
+  char data_buffer[10] = { 0 };
   ssize_t res;
 
   res = tftp_write(

testsuites/libtests/POSIX/free.c

@@ -12,9 +12,10 @@
 
 #include <stdlib.h>
 
+void* p;
+
 int main (void)
 {
-  free((void *) 42);
-
+  free(p);
   return 0;
 }