powerpc/mpic: Use bitmap_zalloc() when applicable

'mpic->protected' is a bitmap. So use 'bitmap_zalloc()' to simplify
code and improve the semantic, instead of hand writing it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/aa145f674e08044c98f13f1a985faa9cc29c3708.1639777976.git.christophe.jaillet@wanadoo.fr

arch/powerpc/sysdev/mpic.c

@@ -1323,8 +1323,7 @@ struct mpic * __init mpic_alloc(struct device_node *node,
 	psrc = of_get_property(mpic->node, "protected-sources", &psize);
 	if (psrc) {
 		/* Allocate a bitmap with one bit per interrupt */
-		unsigned int mapsize = BITS_TO_LONGS(intvec_top + 1);
-		mpic->protected = kcalloc(mapsize, sizeof(long), GFP_KERNEL);
+		mpic->protected = bitmap_zalloc(intvec_top + 1, GFP_KERNEL);
 		BUG_ON(mpic->protected == NULL);
 		for (i = 0; i < psize/sizeof(u32); i++) {
 			if (psrc[i] > intvec_top)