common/rc: re-fix detection of device-mapper/persistent memory incompatibility

common/rc: re-fix detection of device-mapper/persistent memory incompatibility

In commit e05491b3, I tried to resolve false test failures that were
a result of device mapper refusing to change access modes on a block
device that supports the FSDAX access mode.  Unfortunately, I did
not realize that there are two ways that fsdax support can be
detected via sysfs: /sys/block/XXX/queue/dax and /sys/block/XXX/dax/,
so I only added a test for the latter.

As of 5.15-rc1 this doesn't seem to work anymore for some reason.  I
don't know enough about the byzantine world of pmem device driver
initialization, but fsdax mode actually does work even though the
/sys/block/XXX/dax/ path went away.  So clearly we have to detect it
via the other sysfs path.

Fixes: e05491b3 ("common/rc: fix detection of device-mapper/persistent memory incompatibility")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>