thunderbolt: Use kcalloc

The advantage of kcalloc is, that will prevent integer overflows
which could result from the multiplication of number of elements
and size and it is also a bit nicer to read.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Acked-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>