osst: use noop_llseek() instead of default_llseek()

__os_scsi_tape_open() suggests that llseek() doesn't work: "We really want
to do nonseekable_open(inode, filp); here, but some versions of tar
incorrectly call lseek on tapes and bail out if that fails.  So we
disallow pread() and pwrite(), but permit lseeks."

Instead of using the fallback default_llseek() the driver should use
noop_llseek() which leaves the file->f_pos untouched but succeeds.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Willem Riede <osst@riede.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>