[Coverity CID :188890]Insecure data handling in /drivers/watchdog/wdt_qmsi.c

[mandarcthorat1]

Static code scan issues seen in File: /drivers/watchdog/wdt_qmsi.c
Category: Insecure data handling
Function: get_timeout
Component: Drivers
CID: 188890
Please fix or provide comments to square it off in coverity in the link: https://scan9.coverity.com/reports.htm#v32951/p12996

[maxxlife]

@nashif Hi. Do you think that it is a good idea to fix that defect by writing a new function sat_subtract and perform a saturating subtract?
As I understand the issue is count - 1 and its ability to underflow if count=0.

Please check my code idea prototype for that fix:
extern int sat_subtract(u32_t a, u32_t b);
inline sat_subtract(u32_t a, u32_t b)
{
return ((a > b) ? (a - b) : 0);
}
static u32_t get_timeout(u32_t timeout)
{
u32_t count = 0U;
return sat_subtract(count,1U);
}