scsi: hisi_sas: Remove some useless code in hisi_sas_alloc()

The 'hisi_hba->slot_index_tags' bitmap is allocated with bitmap_zalloc() so
it is already cleared. There is no need to clear it another time, one bit
at a time.

Remove the corresponding useless code.

Link: https://lore.kernel.org/r/41c86e7e3e05a13bd586d8ee1b81296140b7a6eb.1637961191.git.christophe.jaillet@wanadoo.fr


Acked-by: John Garry <john.garry@huawei.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>