utils: omnia-mcutool: Bump to 0.3-rc3

utils: omnia-mcutool: Bump to 0.3-rc3

Bump omnia-mcutool to 0.3-rc3:

* The `--upgrade` option will now work even if MCU is in bootloader (for
  example if previous upgrade was aborted).

* On boards with GD32 MCUs, `omnia-mcutool` will now refuse to upgrade
  application firmware to version lower than 4.1 if bootloader version
  is 2.0 (the original for first batch of boards with GD32 MCUs) since
  these versions of application and bootloader are not compatible.

  If user already upgraded to such a combination, an upgrade of
  bootloader firmware is required.

  The `--upgrade` option will inform about this and will automatically
  upgrade bootloader firmware if the `--force` option is given.

  (Note that version 4.1 of the MCU firmware was will be released soon,
   once it is properly tested.)

* Various other improvements.

Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://github.com/openwrt/openwrt/pull/16086
Signed-off-by: Robert Marko <robimarko@gmail.com>