dmaengine: sh: Use bitmap_zalloc() when applicable

'shdma_slave_used' is a bitmap. So use 'bitmap_zalloc()' to simplify code,
improve the semantic and avoid some open-coded arithmetic in allocator
arguments.

Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/3efaf2784424ae3d7411dc47f8b6b03e7bb8c059.1637702701.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/sh/shdma-base.c

@@ -1042,9 +1042,7 @@ EXPORT_SYMBOL(shdma_cleanup);
 
 static int __init shdma_enter(void)
 {
-	shdma_slave_used = kcalloc(DIV_ROUND_UP(slave_num, BITS_PER_LONG),
-				   sizeof(long),
-				   GFP_KERNEL);
+	shdma_slave_used = bitmap_zalloc(slave_num, GFP_KERNEL);
 	if (!shdma_slave_used)
 		return -ENOMEM;
 	return 0;
@@ -1053,7 +1051,7 @@ module_init(shdma_enter);
 
 static void __exit shdma_exit(void)
 {
-	kfree(shdma_slave_used);
+	bitmap_free(shdma_slave_used);
 }
 module_exit(shdma_exit);