WaResultsCollector: fix no kernel path case
WaResultsCollector: fix no kernel path case

If no kernel path has been defined, kernel_refs is empty and
df['kernel_sha1'].replace(kernel_refs) fails

Add sha1 as kernel ref in case no kernel path is provied

Signed-off-by: Vincent Guittot <eb7d4bc75c19026be4afbcab4b7b388cf01677ff@linaro.org>

credp/lisa,credp/lisa,ARM-software/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa