util/cbfstool: free buffer on error path

Fix memory leak found by scan-build from clang version 3.2-11.

Change-Id: Id8f9db46cf42012a0eb0a632c9d83a4eec1989a2
Signed-off-by: Daniele Forsi <dforsi@gmail.com>
Reviewed-on: http://review.coreboot.org/6379
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

util/cbfstool/cbfs-mkstage.c

@@ -134,6 +134,7 @@ int parse_elf_to_stage(const struct buffer *input, struct buffer *output,
 			ERROR("Underflow copying out the segment."
 			      "File has %zu bytes left, segment end is %zu\n",
 			      input->size, (size_t)(phdr[i].p_offset + phdr[i].p_filesz));
+			free(buffer);
 			return -1;
 		}
 		memcpy(buffer + (l_start - data_start),