pinctrl: SPEAr3xx: correct register space to configure pwm

To have pwm on pad no. 34 we also need to select between pwm and SD_LED
functions. Add this to pwm pin mux register configuration.

Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Vipin Kumar <vipin.kumar@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>