fsi: occ: Force sequence numbering per OCC

Set and increment the sequence number during the submit operation.
This prevents sequence number conflicts between different users of
the interface. A sequence number conflict may result in a user
getting an OCC response meant for a different command. Since the
sequence number is now modified, the checksum must be calculated and
set before submitting the command.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210721190231.117185-2-eajames@linux.ibm.com
Signed-off-by: Joel Stanley <joel@jms.id.au>