Fix efsck on boot partition for ppc64le
A previous change to make the PreP partition as the first partition for ppc64le
broke openstack image generation.
@@ -61,7 +61,8 @@ fi
# reflink-backed file on the host https://github.com/coreos/coreos-assembler/pull/935
# and this will verify whether it happened
coreos_gf umount-all
-coreos_gf e2fsck /dev/sda1 correct:false forceall:true
+bootpn=$(coreos_gf findfs-label boot)
+coreos_gf e2fsck "${bootpn}" correct:false forceall:true
coreos_gf_shutdown
