Add MAG271C support

[timschneeb]

Essentially the same as MAG271CR, except no mystic LEDs.

Output of ./msigd --info --debug --query after applying the change:

DEBUG: Initializing HID lib
DEBUG: Found <MSI Gaming Controller> with serial <A02018011700>
Vendor Id:      0x1462
Product Id:     0x3fa4
Product:        MSI Gaming Controller
Serial:         A02018011700
Monitor Series: MAG271C
LED support:    None
s140:           <003>
s150:           <V18>
DEBUG: Special 01 b0: 01 5a 15 00 00 00 00 00 00 00 00 00 00 00 00 00
DEBUG: Special 01 b4: 01 5a 02 02 35 e8 00 00 00 00 00 00 00 00 00 00
macro_key : '000'
serial : 'FA6T028260719'
frequency : '120'
game_mode : '000'
black_tuner : '009'
response_time : '000'
enable_dynamic : '000'
hdcr : '000'
refresh_display : '000'
refresh_position : '000'
alarm_clock : '000'
alarm_position : '000'
screen_assistance : '000'
free_sync : '001'
pro_mode : '000'
eye_saver : '000'
image_enhancement : '000'
brightness : '065'
contrast : '062'
sharpness : '000'
color_preset : '002'
color_red : '050'
color_green : '050'
color_blue : '050'
color_rgb : 'bbb'
input : '001'
osd_language : '001'
osd_transparency : '000'
osd_timeout : '020'
sound_enable : '001'
navi_up : '002'
navi_down : '003'
navi_left : '001'
navi_right : '005'

[timschneeb]

I also added a new entry for the MAG271C with special code "003" to the README.

However, there's already an (empty) entry for the same model with special code "002". I left that one unmodified.