drivers: watchdog: npcx: fix T0 timer reload procedure

The correct procedure to reload the T0 timer is:
    1. Load TWDT0 register with the new value or write 1 to RST bit in
       T0CSR register to load the old value.
    2. Wait until RST bit in T0CSR register becomes 1.
    3. Wait until RST bit in T0CSR register becomes 0.
The current watchdog driver misses step 2.
Fix the issue in this commit.

Signed-off-by: Jun Lin <CHLin56@nuvoton.com>