remoteproc: qcom_q6v5_mss: Provide errors for firmware-name parsing

Failing to read the "firmware-name" DT property without informing the
developer is annoying, add some helpful debug prints.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210312002605.3273255-1-bjorn.andersson@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>