Return the correct value for rgb_color in get_pixel_rgb

[leewillis77]

Fixes the issue where get_pixel_rgb() returns an incorrect value for rgb_color due to a bit-shifting error.

Script to show the issue:

#!/usr/bin/python3

from apa102_pi.driver import apa102

strip = apa102.APA102(30, 'rgb')
strip.clear_strip()
strip.set_pixel_rgb(1, 8421504, bright_percent=100)
stored_data = strip.get_pixel_rgb(1)
print('color returned: ' + str(stored_data['rgb_color']))

The expected output is: color returned: 8421504

The actual output is: color returned: 32896

[leewillis77]

Thanks for the quick merge & release!