staging: exfat: replace kmalloc with kmalloc_array

Replace expressions of the form:
	kmalloc(count * size, GFP_KERNEL);
With:
	kmalloc_array(count, size, GFP_KERNEL);

Signed-off-by: Roi Martin <jroi.martin@gmail.com>
Link: https://lore.kernel.org/r/20191031123139.32361-1-jroi.martin@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>