xfs_repair: find and clobber rtgroup bitmap and summary files

xfs_repair: find and clobber rtgroup bitmap and summary files

On a rtgroups filesystem, if the rtgroups bitmap or summary files are
garbage, we need to clear the dinode and update the incore bitmap so
that we don't bother to check the old rt freespace metadata.

However, we regenerate the entire rt metadata directory tree during
phase 6.  If the bitmap and summary files are ok, we still want to clear
the dinode, but we can still use the incore inode to check the old
freespace contents.  Split the clear_dinode function into two pieces,
one that merely zeroes the inode, and the old clear_dinode now turns off
checking.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>