Dell S6100: Watchdog - Fix Python3 incompatibility (#6734)

To make watchdog.arm() method python3 compatible in DellEMC S6100.

Author: ArunSaravananBalachandran

platform/broadcom/sonic-platform-modules-dell/s6100/sonic_platform/watchdog.py

@@ -151,9 +151,9 @@ def arm(self, seconds):
         if self.is_armed():
             gpio_val = self._read_gpio_file(gpio)
             high_val = gpio_val | (1 << 15)
-            if self._write_gpio_file(gpio, hex(high_val)) != -1:
+            if self._write_gpio_file(gpio, hex(high_val).encode('utf-8')) != -1:
                 low_val = high_val & 0xFFFF7FFF
-                if self._write_gpio_file(gpio, hex(low_val)) != -1:
+                if self._write_gpio_file(gpio, hex(low_val).encode('utf-8')) != -1:
                     self.armed_time = self._get_time()
                     self.timeout = seconds
                     return seconds