firmware: turris-mox-rwtm: report failures better

firmware: turris-mox-rwtm: report failures better

Report a notice level message if a command is not supported by the rWTM
firmware.

This should not be an error, merely a notice, because the firmware can
be used on boards that do not have manufacturing information burned.

Fixes: 389711b37493 ("firmware: Add Turris Mox rWTM firmware driver")
Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>