examples/nxplayer: fix build error when CONFIG_AUDIO_FORMAT_MIDI=y
examples/nxplayer: fix build error when CONFIG_AUDIO_FORMAT_MIDI=y

nxplayer_getmidisubformat() did not consider default case in the switch
statement.

Change-Id: I8e0fb2d2c72caab8038eaddeb5886128e0037051
Signed-off-by: Bongryul Lee <40e5879ba2a710c5c582426d4fb9229bced4a8b1@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT