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

Cc: Richard Fontana <rfontana@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Allison Randal <allison@lohutok.net>
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>