coccinelle: don't run iovec-make on iovec_done{,_erase}

coccinelle: don't run iovec-make on iovec_done{,_erase}

As the result is a bit funky (but still valid), i.e.:

 static inline void iovec_done_erase(struct iovec *iovec) {
         assert(iovec);

-        iovec->iov_base = erase_and_free(iovec->iov_base);
-        iovec->iov_len = 0;
+        *iovec = IOVEC_MAKE(erase_and_free(iovec->iov_base), 0);
 }