coresight: etb10: Fix check for bogus buffer depth

coresight: etb10: Fix check for bogus buffer depth

We attempt to sanity check the buffer depth reported by the hardware by
making sure it is not less than zero however this check will never be true
since the buffer depth is stored in an unsigned integer. Instead change
the check to look for the top bit being set which was the intention.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>