[packages] firmwarehotplug: make source compatible with sdcc 3.x

fix build errors of firmwarehotplug caused by switch of sdcc from 2.x to 3.x

errors were:
./ezusb_reg.h:26: syntax error: token -> 'at' ; column 7

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>