[Unicast] Update the icons in LEA device settings as headphones icon

This is the step#1 at comment, changing ic_bt_le_audio.xml to the
same icon as ic_bt_headset_hfp.xml so that we display all LE audio
devices as headphones for now because right now all LE audio devices
are earbuds or headphones.

Bug: 258009444
Test: build pass
Change-Id: I1bc037a8a1ab9a2836016333f4683b48d1384303