Make use of the newly introduce mallocarray(9).

[pfg]

Summary

Not sure there is any chance of an overflow here but perhaps this also
makes the code easier to read.

[erj]

Why didn't they provide a calloc(), to follow the malloc()/free() pattern?

(It looks like this was introduced in rS327674)

[erj]

In D13833#290191, @erj wrote:

Why didn't they provide a calloc(), to follow the malloc()/free() pattern?

(It looks like this was introduced in rS327674)

And I forgot that not everyone wants the memory they allocate to be zeroed, though the driver zeroes it in all of the calls that are being replaced here.