Eliminate several cases of multiplication in arguments to calloc

Eliminate several cases of multiplication in arguments to calloc

In commit 32f2fd1c5d6088692551c80352b7d6fa35b0cd09, several calls to
_mesa_calloc(x) were replaced with calls to calloc(1, x). This is strictly
equivalent to what the code was doing previously.

But for cases where "x" involves multiplication, now that we are explicitly
using the two-argument calloc, we can do one step better and replace:

	calloc(1, A * B);

with:

	calloc(A, B);

The advantage of the latter is that calloc will detect any overflow that would
have resulted from the multiplication and will fail the allocation, (whereas
the former would return a small allocation). So this fix can change
potentially exploitable buffer overruns into segmentation faults.

Reviewed-by: Matt Turner <mattst88@gmail.com>