Commit a885c8c4 that introduced the
getgeo block device method changed the fallback number of sectors and
introduced a bug into the fallback cylinder number calculation.

Thanks to Rusty Russell for noticing this.
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>