Switch to bitmap_zalloc() to show clearly what we are allocating.
Besides that it returns pointer of bitmap type instead of opaque void *.

Link: http://lkml.kernel.org/r/20190304100009.65147-1-andriy.shevchenko@linux.intel.com
To: linux-kernel@vger.kernel.org
To: Andrew Morton <akpm@linux-foundation.org>
To: linux@rasmusvillemoes.dk
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>