coresight: Use devm_bitmap_zalloc when applicable

'drvdata->chs.guaranteed' is a bitmap. So use 'devm_bitmap_kzalloc()' to
simplify code, improve the semantic and avoid some open-coded arithmetic
in allocator arguments.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/a4b8454f560b70cedf0e4d06275787f08d576ee5.1635964610.git.christophe.jaillet@wanadoo.frSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

drivers/hwtracing/coresight/coresight-stm.c

@@ -856,13 +856,11 @@ static int stm_probe(struct amba_device *adev, const struct amba_id *id)
 {
 	int ret;
 	void __iomem *base;
-	unsigned long *guaranteed;
 	struct device *dev = &adev->dev;
 	struct coresight_platform_data *pdata = NULL;
 	struct stm_drvdata *drvdata;
 	struct resource *res = &adev->res;
 	struct resource ch_res;
-	size_t bitmap_size;
 	struct coresight_desc desc = { 0 };
 
 	desc.name = coresight_alloc_device_name(&stm_devs, dev);
@@ -904,12 +902,10 @@ static int stm_probe(struct amba_device *adev, const struct amba_id *id)
 	else
 		drvdata->numsp = stm_num_stimulus_port(drvdata);
 
-	bitmap_size = BITS_TO_LONGS(drvdata->numsp) * sizeof(long);
-
-	guaranteed = devm_kzalloc(dev, bitmap_size, GFP_KERNEL);
-	if (!guaranteed)
+	drvdata->chs.guaranteed = devm_bitmap_zalloc(dev, drvdata->numsp,
+						     GFP_KERNEL);
+	if (!drvdata->chs.guaranteed)
 		return -ENOMEM;
-	drvdata->chs.guaranteed = guaranteed;
 
 	spin_lock_init(&drvdata->spinlock);