vppinfra: fix coverity issue 205691 in pmalloc

set the address to MMAP_FAILED if mmap has failed,
so that we do not attempt to free it in the error
handling path.

Change-Id: I6e6b51a365fb68086dc20aa40a676a36af59a3ba
Type: fix
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>

src/vppinfra/pmalloc.c

@@ -331,6 +331,7 @@ pmalloc_map_pages (clib_pmalloc_main_t * pm, clib_pmalloc_arena_t * a,
       pm->error = clib_error_return_unix (0, "failed to mmap %u pages at %p "
 					  "fd %d numa %d flags 0x%x", n_pages,
 					  va, a->fd, numa_node, mmap_flags);
+      va = MAP_FAILED;
       goto error;
     }