staging: nvec: remove use of clk_get_sys

As clock information is added to device tree clock can be looked up
using clk_get. Remove use of clk_get_sys.

Signed-off-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Acked-by: Julian Andres Klode <jak@jak-linux.org>
[swarren: updated TODO file to remove entry that requested this change]
Signed-off-by: Stephen Warren <swarren@nvidia.com>