pwm: mediatek: Prevent divide-by-zero in pwm_mediatek_config()

With CONFIG_COMPILE_TEST && !CONFIG_HAVE_CLK, pwm_mediatek_config() has a
divide-by-zero in the following line:

	do_div(resolution, clk_get_rate(pc->clk_pwms[pwm->hwpwm]));

due to the fact that the !CONFIG_HAVE_CLK version of clk_get_rate()
returns zero.

This is presumably just a theoretical problem: COMPILE_TEST overrides
the dependency on RALINK which would select COMMON_CLK.  Regardless it's
a good idea to check for the error explicitly to avoid divide-by-zero.

Fixes the following warning:

  drivers/pwm/pwm-mediatek.o: warning: objtool: .text: unexpected end of section

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/fb56444939325cc173e752ba199abd7aeae3bf12.1742852847.git.jpoimboe@kernel.org


[ukleinek: s/CONFIG_CLK/CONFIG_HAVE_CLK/]
Fixes: caf065f8 ("pwm: Add MediaTek PWM support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/9e78a0796acba3435553ed7db1c7965dcffa6215.1743501688.git.u.kleine-koenig@baylibre.com


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>