Since the QMP driver split there will be precisely two child nodes so
drop the obsolete iteration construct.

While at it, drop the verbose error logging that would have been printed
also on probe deferrals.

Note that there is no need to check if there are additional child nodes
(the kernel is not a devicetree validator), but let's return an error if
either child node is missing.
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20221114110621.4639-21-johan+linaro@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>