ip2: fix compiler warning on ip2main_pci_tbl

Annotate ip2main_pci_tbl as '__used' to fix following warning:

  CC      drivers/char/ip2/ip2main.o
drivers/char/ip2/ip2main.c:3227: warning: ‘ip2main_pci_tbl’ defined but not used

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: "Michael H. Warfield" <mhw@wittsend.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>