clocksource/drivers/tegra186: Avoid 64-bit division

clocksource/drivers/tegra186: Avoid 64-bit division

The newly added function causes a build failure on 32-bit targets with
older compiler version such as gcc-10:

arm-linux-gnueabi-ld: drivers/clocksource/timer-tegra186.o: in function `tegra186_wdt_get_timeleft':
timer-tegra186.c:(.text+0x3c2): undefined reference to `__aeabi_uldivmod'

The calculation can trivially be changed to avoid the division entirely,
as USEC_PER_SEC is a multiple of 5. Change both such calculation for
consistency, even though gcc apparently managed to optimize the other one
properly already.

[dlezcano : Fixed conflict with 20250614175556.922159-2-linux@roeck-us.net ]

Fixes: 28c842c8b0f5 ("clocksource/drivers/timer-tegra186: Add WDIOC_GETTIMELEFT support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20250620111939.3395525-1-arnd@kernel.org