floss: avrcp: uinput: return result and error message when init uniput

Similar to send_key, the initialization should return a result instead
of printing an error log on the scene without return. This creates a
more flexible error handling for the caller.

Bug: 240780817
Tag: #floss
Test: emerge-${BOARD} floss

Change-Id: I19431239b7c8441833c0440827dcf1ea0bf488ff