niu: fix another warning in drivers/net/niu.c

this warning:

  drivers/net/niu.c: In function ‘esr_reset’:
  drivers/net/niu.c:741: warning: ‘reset’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between:

 - esr_read_reset() and 'reset'

Annotate it.

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