staging/rtl8192u: Prefer kcalloc over open coded arithmetic

staging/rtl8192u: Prefer kcalloc over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

In this case these aren't actually dynamic sizes: both sides of the
multiplication are constant values. However it is best to refactor these
anyway, just to keep the open-coded math idiom out of code.

So, use the purpose specific kcalloc() function instead of the argument
size * count in the kzalloc() function.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Len Baker <len.baker@gmx.com>
Link: https://lore.kernel.org/r/20210824090039.GA7999@titan
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>