Ignore target memories not present in part

$ avrdude -qp m8 -c ... -U efuse:w:0xff:m && echo OK

avrdude: AVR device initialized and ready to accept instructions
avrdude: skipping -U efuse:... as memory not defined for part ATmega8

avrdude done.  Thank you.

OK

src/main.c

@@ -1243,7 +1243,7 @@ int main(int argc, char * argv [])
   for (ln=lfirst(updates); ln; ln=lnext(ln)) {
     upd = ldata(ln);
     rc = do_op(pgm, p, upd, uflags);
-    if (rc) {
+    if (rc && rc != LIBAVRDUDE_SOFTFAIL) {
       exitrc = 1;
       break;
     }