classes/image_types_wic: Reorder do_flush_pseudodb

When IMAGE_FSTYPES contains more types than wic, it can happen than the
pseudo database is not flushed properly.

This can be solved by changing the order of when do_flush_pseudodb is
launched.

Yocto Bug: https://bugzilla.yoctoproject.org/show_bug.cgi?id=13898


Fixes: dde90a5d ("wic: Fix multi images .wks with bitbake")
Signed-off-by: Ricardo Ribalda <ricardo@ribalda.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 445b0a95)
Signed-off-by: Steve Sakoman <steve@sakoman.com>