pinctrl: st: remove gpiochip in failure cases

This patch releases gpiochip related resources by calling
gpiochip_remove when gpiochip_irqchip_add fails.

Cc: Maxime Coquelin <maxime.coquelin@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>