defxx: fix build warning

We are getting many build warnings about:
'bar_start' may be used uninitialized
and
'bar_len' may be used uninitialized

They are not actually uninitialized as dfx_get_bars() will initialize
them properly. But still lets have them initialized just to satisfy the
compiler (gcc 4.8.2).

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>