pinctrl/nomadik: fix null in irqdomain errorpath

The irqdomain conversion failed to notice that we do not always
have a DT node to dereference, fix this up by using a simple
dev_err() that also tells the name of the device.

Cc: Loic Pallardy <loic.pallardy@st.com>
Cc: Patrice Chotard <patrice.chotard@stericsson.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>