xfs_quota: fix false error reporting of project inheritance flag is not set

xfs_quota: fix false error reporting of project inheritance flag is not set

After kernel commit:

9336e3a7 "xfs: project id inheritance is a directory only flag"

xfs stopped setting the project inheritance flag on regular files, but
userspace quota code still checks for it and will now issue the error:

"project inheritance flag is not set"

for every regular file during quotacheck.  Fix this by only checking
for the flag on directories.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1663502
Reported-by: Steven Gardner <sgardner@redhat.com>
Signed-off-by: Achilles Gaikwad <agaikwad@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>