rtc: tps6594: Fix integer overflow on 32bit systems

rtc: tps6594: Fix integer overflow on 32bit systems

The problem is this multiply in tps6594_rtc_set_offset()

	tmp = offset * TICKS_PER_HOUR;

The "tmp" variable is an s64 but "offset" is a long in the
(-277774)-277774 range.  On 32bit systems a long can hold numbers up to
approximately two billion.  The number of TICKS_PER_HOUR is really large,
(32768 * 3600) or roughly a hundred million.  When you start multiplying
by a hundred million it doesn't take long to overflow the two billion
mark.

Probably the safest way to fix this is to change the type of
TICKS_PER_HOUR to long long because it's such a large number.

Fixes: 9f67c1e63976 ("rtc: tps6594: Add driver for TPS6594 RTC")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/1074175e-5ecb-4e3d-b721-347d794caa90@stanley.mountain
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>