watchdog: alim1535_wdt: fix compiler warning on ali_pci_tbl

Annotate ali_pci_tbl as '__used' to fix following warning:

  CC      drivers/watchdog/alim1535_wdt.o
drivers/watchdog/alim1535_wdt.c:304: warning: ‘ali_pci_tbl’ defined but not used

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>