platform/mellanox: Use 2-factor allocator calls

As already done treewide, switch from open-coded multiplication to using
2-factor allocation helpers.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>