macintosh/mac_hid: add MODULE_DESCRIPTION()

Fix the make W=1 warning:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/macintosh/mac_hid.o

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
[mpe: Change the description to just "Mouse button 2+3 emulation"]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240509-mac_hid-md-v1-1-4091f1e4e4e0@quicinc.com