pwm: imx-tpm: Use 64-bit division macro

pwm: imx-tpm: Use 64-bit division macro

Since the PWM framework is switching struct pwm_state.period's datatype
to u64, prepare for this transition by using DIV64_U64_ROUND_CLOSEST to
handle a 64-bit divisor.

Cc: Shawn Guo <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Pengutronix Kernel Team <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: NXP Linux Team <[email protected]>
Signed-off-by: Guru Das Srinagesh <[email protected]>
Signed-off-by: Thierry Reding <[email protected]>