remoteproc: Restructure firmware name allocation

Improve the readability of function rproc_alloc_firmware() by using
a non-negated condition and moving the comment out of the conditional
block

Suggested-by: Alex Elder <elder@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200420231601.16781-3-mathieu.poirier@linaro.org


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