staging.bbclass: process direct dependencies in deterministic order

* this doesn't fix any issue (at least AFAIK),
  just keeps the log files more deterministic to avoid unnecessary churn like in:

  --- /OE/build/oe-core/tmp-glibc/work/qemux86_64-oe-linux/keymaps/1.0-r31/temp/log.do_patch.2213051      2022-05-26 11:35:44.110063749 +0200
  +++ /OE/build/oe-core/tmp-glibc/work/qemux86_64-oe-linux/keymaps/1.0-r31/temp/log.do_patch.2213372      2022-05-26 11:35:54.553062630 +0200
  @@ -1,7 +1,7 @@
   DEBUG: Executing python function extend_recipe_sysroot
  -NOTE: Direct dependencies are ['virtual:native:/OE/build/oe-core/openembedded-core/meta/recipes-devtools/patch/patch_2.7.6.bb:do_populate_sysroot', '/OE/build/oe-core/openembedded-core/meta/recipes-devtools/quilt/quilt-native_0.67.bb:do_populate_sysroot']
  +NOTE: Direct dependencies are ['/OE/build/oe-core/openembedded-core/meta/recipes-devtools/quilt/quilt-native_0.67.bb:do_populate_sysroot', 'virtual:native:/OE/build/oe-core/openembedded-core/meta/recipes-devtools/patch/patch_2.7.6.bb:do_populate_sysroot']
   NOTE: Installed into sysroot: []
  -NOTE: Skipping as already exists in sysroot: ['patch-native', 'quilt-native', 'attr-native', 'libtool-native', 'gettext-minimal-native', 'texinfo-dummy-native']
  +NOTE: Skipping as already exists in sysroot: ['quilt-native', 'patch-native', 'attr-native', 'libtool-native', 'gettext-minimal-native', 'texinfo-dummy-native']
   DEBUG: Python function extend_recipe_sysroot finished
   DEBUG: Executing python function do_patch
   DEBUG: Executing python function patch_do_patch

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit d3ebb37b)
Signed-off-by: Steve Sakoman <steve@sakoman.com>