pinctrl: error if mapping table's control dev can't be found

This is a serious error, and the pin control system will not function
correctly if it ends up not programing the mapping table entries into
the HW. Instead of just ignoring this, error out.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
[rebased to fit the applied patch series, cast error to pointer]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>