pwm: spear: Remove unused *dev from struct spear_pwm_chip

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Shiraz Hashim <shiraz.hashim@st.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>