scsi: ses: Fix wrong page error

If a SES device returns an error on a requested diagnostic page, we are
currently printing an error indicating the wrong page was received. Fix
this up to simply return a failure and only check the returned page when
the diagnostic page buffer was populated by the device.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>