sparc32: Fix might-be-used-uninitialized warning in do_sparc_fault().

When we try to handle vmalloc faults, we can take a code
path which uses "code" before we actually set it.

Amusingly gcc-3.3 notices this yet gcc-4.x does not.

Reported-by: Bob Breuer <breuerr@mc.net>
Signed-off-by: David S. Miller <davem@davemloft.net>