remoteproc: Simplify default name allocation

remoteproc: Simplify default name allocation

In an effort to cleanup firmware name allocation, replace the
cumbersome mechanic used to allocate a default firmware name with
function kasprintf().

Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Suggested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200415204858.2448-4-mathieu.poirier@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>