raid6check.c: reduce verbosity

This patch removes some printouts, which
are not really useful here.
These could be re-added later, in case a
verbosity parameter will be provided.

Signed off: piergiorgio.sartor@nexgo.de

Signed-off-by: NeilBrown <neilb@suse.de>
raid6check.c: fix position printout

This patch make a bit more clear
the position, in the disk, where
an error is found.

Signed off: piergiorgio.sartor@nexgo.de

Signed-off-by: NeilBrown <neilb@suse.de>
raid6check.c: fix Q parity generation

In the transition to 4K page processing,
the Q parity generation had a wrong offset
in the buffer.
This patche fix this.

Signed off: piergiorgio.sartor@nexgo.de

Signed-off-by: NeilBrown <neilb@suse.de>
raid6check.c: add O_SYNC to open

It could be better to make sure the
data reaches the disks, so open the
drives with O_SYNC flag.

Signed off: piergiorgio.sartor@nexgo.de

Signed-off-by: NeilBrown <neilb@suse.de>