pinctrl: Drop error prints on kzalloc() failure

Upon failing kzalloc() will print an error message in the log, so
there's no need for additional printouts. Also standardizes the "!ptr"
vs "ptr == NULL" while I'm touching those lines.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>