wwan: core: Use the bitmap API to allocate bitmaps

Use bitmap_zalloc() and bitmap_free() instead of hand-writing them.
It is less verbose and it improves the type checking and semantic.

While at it, add missing header inclusion (should be bitops.h,
but with the above change it becomes bitmap.h).
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230911131618.4159437-1-andriy.shevchenko@linux.intel.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/wwan/wwan_core.c

 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright (c) 2021, Linaro Ltd <loic.poulain@linaro.org> */
 
+#include <linux/bitmap.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/debugfs.h>
@@ -395,7 +396,7 @@ static int __wwan_port_dev_assign_name(struct wwan_port *port, const char *fmt)
 	char buf[0x20];
 	int id;
 
-	idmap = (unsigned long *)get_zeroed_page(GFP_KERNEL);
+	idmap = bitmap_zalloc(max_ports, GFP_KERNEL);
 	if (!idmap)
 		return -ENOMEM;
 
@@ -414,7 +415,7 @@ static int __wwan_port_dev_assign_name(struct wwan_port *port, const char *fmt)
 
 	/* Allocate unique id */
 	id = find_first_zero_bit(idmap, max_ports);
-	free_page((unsigned long)idmap);
+	bitmap_free(idmap);
 
 	snprintf(buf, sizeof(buf), fmt, id);	/* Name generation */