Unused variable warning in SAMD51 implementation

[IanBurwell]

When compiling for the PyPortal (SAMD51) GCC raises an unused variable warning (see below). This issue is not critical but would be easily fixed by removing the hanging bit variable here

GCC (9.3.1) warns the following:

.pio/libdeps/adafruit_pyportal_m4_titano/Adafruit NeoPixel/Adafruit_NeoPixel.cpp: In member function 'void Adafruit_NeoPixel::show()':
.pio/libdeps/adafruit_pyportal_m4_titano/Adafruit NeoPixel/Adafruit_NeoPixel.cpp:2505:44: warning: unused variable 'bit' [-Wunused-variable]
 2505 |   uint8_t *ptr, *end, p, bitMask, portNum, bit;
      |                                            ^~~