qla3xxx: fix warning in drivers/net/qla3xxx.c

this warning:

  drivers/net/qla3xxx.c: In function ‘ql3xxx_probe’:
  drivers/net/qla3xxx.c:3912: warning: ‘pci_using_dac’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between 'pci_using_dac' and 'err'.

Annotate it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>