scsi: st: Remove redundant variable pointer stp

Variable stp is assigned a value that is never read, the assignment and the
variable stp are redundant and can be removed.

Cleans up clang scan build warning:

drivers/scsi/st.c:4253:7: warning: Although the value stored to 'stp'
is used in the enclosing expression, the value is never actually
read from 'stp' [deadcode.DeadStores]

Link: https://lore.kernel.org/r/20220805115652.2340991-1-colin.i.king@gmail.com


Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>