drm/amd/display: Increase size of audios array

[Why]
The audios array defined in "struct resource_pool" is only 6 (MAX_PIPES)
but the max number of audio devices (num_audio) is 7. In some projects,
it will run out of audios array.

[How]
Incraese the audios array size to 7.

Signed-off-by: Tai Man <taiman.wong@amd.com>
Reviewed-by: Joshua Aberback <Joshua.Aberback@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>