watchdog: rzg2l_wdt: Fix 32bit overflow issue

In the Linux kernel, the following vulnerability has been resolved:

watchdog: rzg2l_wdt: Fix 32bit overflow issue

The value of timer_cycle_us can be 0 due to 32bit overflow.

For eg:- If we assign the counter value "0xfff" for computing

maxval.

This patch fixes this issue by appending ULL to 1024, so that

it is promoted to 64bit.

This patch also fixes the warning message, 'watchdog: Invalid min and

max timeout values, resetting to 0!'.