greybus: firmware: log the name of the firmware being requested

People are getting confused as to what the firmware file name is for
their module, so log it to make it easier to find modules with "blank"
vid/pid values and let people know what to name their firmware files.

Because we are now logging this, turn the debug message after the
firmware request into an error message if something fails.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Reviewed-by: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>