poky: reset subtree on master HEAD(a88251b3e7)

As part of the last subtree update, I used master-next as the
subtree basis because there was a fix we needed in order to get QEMU
to pass.  I didn't realize that master-next deviated (because they use
to just have short-term patches in it).  Reset the content to the same
fix but from the master branch.

Change-Id: Ic7d2f0ac42e9da3eb263586b26ba56d8798d5bcf
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/poky/meta-selftest/conf/layer.conf b/poky/meta-selftest/conf/layer.conf
index 48ca846..763ea01 100644
--- a/poky/meta-selftest/conf/layer.conf
+++ b/poky/meta-selftest/conf/layer.conf
@@ -11,4 +11,4 @@
 
 addpylib ${LAYERDIR}/lib oeqa
 
-LAYERSERIES_COMPAT_selftest = "scarthgap"
+LAYERSERIES_COMPAT_selftest = "styhead"