Staging: media: atomisp: Use kmalloc_array instead of kmalloc

Prefer kmalloc_array over kmalloc with multiply
because kmalloc_array performs additional checks
before memory allocation.

Fix the following issue reported by checkpatch.pl:
* WARNING: Prefer kmalloc_array over kmalloc with multiply

Signed-off-by: Georgiana Chelu <georgiana.chelu93@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>