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: 9f67c1e ("rtc: tps6594: Add driver for TPS6594 RTC")
Signed-off-by: Dan Carpenter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexandre Belloni <[email protected]>

Author: Dan Carpenter

drivers/rtc/rtc-tps6594.c

@@ -37,7 +37,7 @@
 #define MAX_OFFSET (277774)
 
 // Number of ticks per hour
-#define TICKS_PER_HOUR (32768 * 3600)
+#define TICKS_PER_HOUR (32768 * 3600LL)
 
 // Multiplier for ppb conversions
 #define PPB_MULT NANO