Change do_write_srcrevs to a postfunc of do_fetch, avoiding a dependency
being created that causes large numbers of setscene tasks being executed
on every build with both buildhistory and rm_work being enabled.
(From OE-Core rev: a751e9042dfffcc5c4701634a1f1f598012d609c)
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>