Add MIC mute key which is found on HP Business Slim Keyboard

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 23 Spd=1.5 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=03f0 ProdID=2f4a Rev=00.10
S:  Manufacturer=Chicony
S:  Product=HP Business Slim Keyboard
C:  #Ifs= 2 Cfg#= 1 Atr=a0 MxPwr=100mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=01 Driver=usbhid
I:  If#= 1 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=00 Prot=00 Driver=usbhid
Signed-off-by: NAceLan Kao <acelan.kao@canonical.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>