The driver can match only via the DT table so the table should be always
used and the of_match_ptr does not have any sense (this also allows ACPI
matching via PRP0001, even though it might not be relevant here). This
also fixes the following compile error:

  drivers/pwm/pwm-stm32-lp.c:245:34: error: ‘stm32_pwm_lp_of_match’ defined but not used [-Werror=unused-const-variable=]

for builds with CONFIG_OF=n, CONFIG_PWM_STM32_LP=y and W=1.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>