drivers/neopixel: Reduce code size of driver.

Saves 71 bytes of bytecode.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

drivers/neopixel/neopixel.py

 # NeoPixel driver for MicroPython
 # MIT license; Copyright (c) 2016 Damien P. George, 2021 Jim Mussared
 
-from micropython import const
 from machine import bitstream
 
-_BITSTREAM_TYPE_HIGH_LOW = const(0)
-_TIMING_WS2818_800 = (400, 850, 800, 450)
-_TIMING_WS2818_400 = (800, 1700, 1600, 900)
-
 
 class NeoPixel:
+    # G R B W
     ORDER = (1, 0, 2, 3)
 
     def __init__(self, pin, n, bpp=3, timing=1):
@@ -18,8 +14,10 @@ class NeoPixel:
         self.bpp = bpp
         self.buf = bytearray(n * bpp)
         self.pin.init(pin.OUT)
+        # Timing arg can either be 1 for 800kHz or 0 for 400kHz,
+        # or a user-specified timing ns tuple (high_0, low_0, high_1, low_1).
         self.timing = (
-            (_TIMING_WS2818_800 if timing else _TIMING_WS2818_400)
+            ((400, 850, 800, 450) if timing else (800, 1700, 1600, 900))
             if isinstance(timing, int)
             else timing
         )
@@ -27,21 +25,22 @@ class NeoPixel:
     def __len__(self):
         return self.n
 
-    def __setitem__(self, index, val):
-        offset = index * self.bpp
+    def __setitem__(self, i, v):
+        offset = i * self.bpp
         for i in range(self.bpp):
-            self.buf[offset + self.ORDER[i]] = val[i]
+            self.buf[offset + self.ORDER[i]] = v[i]
 
-    def __getitem__(self, index):
-        offset = index * self.bpp
+    def __getitem__(self, i):
+        offset = i * self.bpp
         return tuple(self.buf[offset + self.ORDER[i]] for i in range(self.bpp))
 
-    def fill(self, color):
-        for i in range(self.bpp):
-            c = color[i]
+    def fill(self, v):
         b = self.buf
+        for i in range(self.bpp):
+            c = v[i]
             for j in range(self.ORDER[i], len(self.buf), self.bpp):
                 b[j] = c
 
     def write(self):
-        bitstream(self.pin, _BITSTREAM_TYPE_HIGH_LOW, self.timing, self.buf)
+        # BITSTREAM_TYPE_HIGH_LOW = 0
+        bitstream(self.pin, 0, self.timing, self.buf)