tools/livepatch: initialise j to 0 to fix compilation error in gcc 4.5

tools/livepatch: initialise j to 0 to fix compilation error in gcc 4.5

Initialise j to 0 to make some versions of gcc (e.g., gcc4.5/4.3) happy to
avoid compilation error by commit beba3693f7243e68bbe31fe3794da91068eeea5b.

Failure manifests with gcc 4.5 as:

[  153s] cc1: warnings being treated as errors
[  153s] xen-livepatch.c: In function 'main':
[  153s] xen-livepatch.c:415:12: error: 'j' may be used uninitialized in this function
[  153s] make[3]: *** [xen-livepatch.o] Error 1

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>