xfs_db: fix unaligned accesses

xfs_db: fix unaligned accesses

Fix 2 unaligned accesses in xfs_db which caused bus errors on
sparc64.  Similar treatment was already done in xfs_repair and
xfs_metadump but somehow xfs_db got missed.

Thanks to Anatoly for reminding me that unaligned access is
a thing.  ;)

Resolves-oss-bugzilla: #1140
Reported-by: Anatoly Pugachev <matorola@gmail.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>