brcmsmac: fix warning in _initvars_srom_pci

  CC [M]  drivers/net/wireless/brcm80211/brcmsmac/srom.o
drivers/net/wireless/brcm80211/brcmsmac/srom.c: In function ‘_initvars_srom_pci’:
drivers/net/wireless/brcm80211/brcmsmac/srom.c:641:6: warning: ‘val’ may be used uninitialized in this function

Signed-off-by: John W. Linville <linville@tuxdriver.com>