If GEOM is idle but the root device is not yet present when we enter
vfs_mountroot_wait_if_necessary, we call vfs_mountroot_wait to wait
for root holds (e.g. CAM or USB initialization). Upon returning from
vfs_mountroot_wait, we wait 100 ms at a time until the root device
shows up.
Since the root device most likely appeared during vfs_mountroot_wait
- waiting for subsystems which may be responsible for the root
device is the whole purpose of that function -- it makes sense to
check if the device is now present rather than printing a warning
and pausing for 100 ms before checking.
Fixes: a3ba3d09c248 Make root mount wait mechanism smarter
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