drm/radeon: properly initialize r600_audio_status() data

The structure returned from r600_audio_status() is only partially
initialized, and older gcc versions (4.3 and 4.4) warn about this:

drivers/gpu/drm/radeon/r600_hdmi.c: In function 'r600_audio_status':
drivers/gpu/drm/radeon/r600_hdmi.c:108: error: 'status.id' is used uninitialized in this function
drivers/gpu/drm/radeon/r600_hdmi.c:108: error: 'status.connected' is used uninitialized in this function
drivers/gpu/drm/radeon/r600_hdmi.c:108: error: 'status.offset' is used uninitialized in this function

This is harmless and surprisingly correct in C99, as the caller
only accesses the fields that got initialized, so newer compilers
don't warn about it, but initializing the entire structure feels
like the right thing to do here and avoids the warning.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>