Commit
0e8856d2 (assemble multidevice btrfs volumes without external
tools (#6607)) introduced a call to udevadm. That lives in @rootbindir@,
not @rootlibexecdir@. So fix the path.
ENV{ID_BTRFS_READY}=="0", ENV{SYSTEMD_READY}="0"
# reconsider pending devices in case when multidevice volume awaits
-ENV{ID_BTRFS_READY}=="1", RUN+="@rootlibexecdir@/udevadm trigger -s block -p ID_BTRFS_READY=0"
+ENV{ID_BTRFS_READY}=="1", RUN+="@rootbindir@/udevadm trigger -s block -p ID_BTRFS_READY=0"
LABEL="btrfs_end"