pinctrl: make "hog" mapping table entries work

Commit 77a59883 "pinctrl: changes hog mechanism to be self-referential"
modified the way "hog" entries were represented in the mapping table.
However, the new representation failed some error checks in
pinctrl_hog_map(). Remove the now-bogus error-check, and fix the code
to solve the issue the error-check used to avoid.

Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>