Fix potential memory overflow in welcome string

stage1.c:354:41: warning: '%s' directive output may be truncated writing up to 127 bytes into a region of size 117 [-Wformat-truncation=]
  snprintf(buf, sizeof(buf), "Welcome to %s", version);
                                         ^~   ~~~~~~~
In file included from /usr/include/stdio.h:862,
                 from stage1.c:30:
/usr/include/bits/stdio2.h:64:10: note: '__builtin___snprintf_chk' output between 12 and 139 bytes into a destination of size 128
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

stage1.c

@@ -340,7 +340,7 @@ void getversion()
 void stage1()
 {
 	enum return_type ret;
-	char buf[128];
+	char buf[256];
 	char *init;
 
 	open_log();