x86/dumpstack: Remove unneeded check in dump_trace()

Smatch complains that we have some inconsistent NULL checking.

If "task" were NULL then it would lead to a NULL dereference
later. We can remove this test because earlier on in the
function we have:

 if (!task)
	task = current;

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Clemens Ladisch <clemens@ladisch.de>
Link: http://lkml.kernel.org/r/20120128105246.GA25092@elgon.mountain


Signed-off-by: Ingo Molnar <mingo@elte.hu>