[SCSI] st: simplify new_tape_buffer

- remove the from_initialization argument, which is always 1. We
always need to use GFP_ATOMIC.

- 'got' valuable is initialized to zero and doesn't change. We don't
need it.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Kai Makisara <Kai.Makisara@kolumbus.fi>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>