ath6kl: fix uninitialized variable in ath6kl_sdio_enable_scatter()

gcc 4.8 warns

/backup/lsrc/git/linux-lto-2.6/drivers/net/wireless/ath/ath6kl/sdio.c:
In function 'ath6kl_sdio_enable_scatter':
/backup/lsrc/git/linux-lto-2.6/drivers/net/wireless/ath/ath6kl/sdio.c:748:16:
warning: 'ret' may be used uninitialized in this function
[-Wmaybe-uninitialized]
  if (virt_scat || ret) {
                ^

The variable can indeed be uninitialized when the previous if branch is
skipped. I just set it to zero for now. I'm not fully sure the fix is
correct, maybe the || should be an && ?

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>