scsi: target: Remove unused variable 'tpg'

Gcc reports warning as follows:

drivers/target/target_core_pr.c:1162:26: warning:
 variable 'tpg' set but not used [-Wunused-but-set-variable]
 1162 |  struct se_portal_group *tpg;
      |                          ^~~

After commit 63c9ffe4 ("scsi: target: Check enforce_pr_isids during
registration"), 'tpg' is never used. Remove it to avoid build warning.

Link: https://lore.kernel.org/r/20200709114636.69256-1-weiyongjun1@huawei.com


Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>