scsi: hisi_sas: Use devm_bitmap_zalloc() when applicable

'hisi_hba->slot_index_tags' is a bitmap. Use 'devm_bitmap_zalloc()' to
simplify code, improve the semantic, and avoid some open-coded arithmetic
in allocator arguments.

Link: https://lore.kernel.org/r/4afa3f71e66c941c660627c7f5b0223b51968ebb.1637961191.git.christophe.jaillet@wanadoo.frAcked-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>

drivers/scsi/hisi_sas/hisi_sas_main.c

@@ -2516,9 +2516,8 @@ int hisi_sas_alloc(struct hisi_hba *hisi_hba)
 	if (!hisi_hba->breakpoint)
 		goto err_out;
 
-	hisi_hba->slot_index_count = max_command_entries;
-	s = hisi_hba->slot_index_count / BITS_PER_BYTE;
-	hisi_hba->slot_index_tags = devm_kzalloc(dev, s, GFP_KERNEL);
+	s = hisi_hba->slot_index_count = max_command_entries;
+	hisi_hba->slot_index_tags = devm_bitmap_zalloc(dev, s, GFP_KERNEL);
 	if (!hisi_hba->slot_index_tags)
 		goto err_out;