Remove const specifier from channelToTC array in analogWrite on SAM

Members of this array are later passed to functions that accept
non-const pointers. These functions probably don't modify their
arguments, so a better solution would be to update those functions to
accept const pointers. However, they look like third-party code, so that
would require changing the code again on every update. Removing const
here fixes at least the compiler warning for now.

This helps towards #1792.

Author: matthijskooijman

Diff for: hardware/arduino/sam/cores/arduino/wiring_analog.c

@@ -293,7 +293,7 @@ void analogWrite(uint32_t ulPin, uint32_t ulValue) {
 		ETCChannel channel = g_APinDescription[ulPin].ulTCChannel;
 		static const uint32_t channelToChNo[] = { 0, 0, 1, 1, 2, 2, 0, 0, 1, 1, 2, 2, 0, 0, 1, 1, 2, 2 };
 		static const uint32_t channelToAB[]   = { 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0 };
-		static const Tc *channelToTC[] = {
+		static Tc *channelToTC[] = {
 			TC0, TC0, TC0, TC0, TC0, TC0,
 			TC1, TC1, TC1, TC1, TC1, TC1,
 			TC2, TC2, TC2, TC2, TC2, TC2 };