Fix random decode failure of BUMPING_A_ericsson_1
This fixes the randomly failing BUMPING_A_ericsson_1. I discovered that we had a left over fill_ringbuffer in queue_buf_src which ended up running concurrently to the call in device_run causing bitstream corruption. In addition to this fix, the kfifo related code in the IRQ handler has been moved into wave5-vpu.c as its an private implementation detail. The interrupt reason is also cleared after handling it, this is what the TRM recommend and felt more logical. wave5_vpu_clear_interrupt_ex() has been removed, as it was no longer used, and had no purpose.