arm64: stacktrace: remove NULL task check from unwind_frame()

Currently, there is a check for a NULL task in unwind_frame(). It is not
needed since all current callers pass a non-NULL task.

There should be no functional change as a result of this patch.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Kalesh Singh <kaleshsingh@google.com> for the series.
Link: https://lore.kernel.org/r/20220413145910.3060139-2-mark.rutland@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>