[Patch] echo/multi.cpp: Fix clang warnings

[mt]

Clang warns 'id < 0' conditons. Since multi_mix_value_info->values[i].id is int32 [1], so I think we may change variable 'id' from uint32 to int32. And I think other audio drivers also need to change.

[1] ​http://cgit.haiku-os.org/haiku/tree/headers/private/media/hmulti_audio.h#n427

/home/haiku/haiku/haiku/src/add-ons/kernel/drivers/audio/echo/multi.cpp:258:10: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                if (id < 0 || id >= card->multi.control_count) {
                    ~~ ^ ~
/home/haiku/haiku/haiku/src/add-ons/kernel/drivers/audio/echo/multi.cpp:300:10: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                if (id < 0 || id >= card->multi.control_count) {
                    ~~ ^ ~
/home/haiku/haiku/haiku/src/add-ons/kernel/drivers/audio/echo/multi.cpp:311:12: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
                                if (id < 0 || id >= card->multi.control_count) {
                                    ~~ ^ ~

[Barrett]

Applied in hrev50375.