[SCSI] Fix VPD inquiry page wrapper

Fix two bugs in the VPD page wrapper:

    - Don't return failure if the user asked for page 0

    - The end of buffer check failed to account for the page header size
      and consequently didn't work

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>