pwm: imx-tpm: Reset counter if CMOD is 0

pwm: imx-tpm: Reset counter if CMOD is 0

As per the i.MX93 TRM, section 67.3.2.1 "MOD register update", the value
of the TPM counter does NOT get updated when writing MOD.MOD unless
SC.CMOD != 0. Therefore, with the current code, assuming the following
sequence:

	1) pwm_disable()
	2) pwm_apply_might_sleep() /* period is changed here */
	3) pwm_enable()

and assuming only one channel is active, if CNT.COUNT is higher than the
MOD.MOD value written during the pwm_apply_might_sleep() call then, when
re-enabling the PWM during pwm_enable(), the counter will end up resetting
after UINT32_MAX - CNT.COUNT + MOD.MOD cycles instead of MOD.MOD cycles as
normally expected.

Fix this problem by forcing a reset of the TPM counter before MOD.MOD is
written.

Fixes: 738a1cfec2ed ("pwm: Add i.MX TPM PWM driver support")
Cc: stable@vger.kernel.org
Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>
Link: https://lore.kernel.org/r/20250728194144.22884-1-laurentiumihalcea111@gmail.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>