pwm: Remove __init initializer for pwm_add_table()

For platforms that don't support DT, some early MFD modules can register
lookup tables. Remove the __init annotation so that this works. This is
similar to gpio_add_lookup_table() which allows late additions.

CC: Samuel Ortiz <sameo@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>