HAL_Chibios: don't unregister shared DMA

the shared DMA handle is a property of the bus, not the device, so
should not be unregistered when the device is removed

libraries/AP_HAL_ChibiOS/I2CDevice.cpp

@@ -59,7 +59,6 @@ I2CDevice::I2CDevice(uint8_t bus, uint8_t address) :
 
 I2CDevice::~I2CDevice()
 {
-    businfo[_busnum].dma_handle->unregister();
     printf("I2C device bus %u address 0x%02x closed\n", 
            (unsigned)_busnum, (unsigned)_address);
     free(pname);

libraries/AP_HAL_ChibiOS/SPIDevice.cpp

@@ -164,7 +164,6 @@ SPIDevice::~SPIDevice()
 {
     //printf("SPI device %s on %u:%u closed\n", device_desc.name,
     //       (unsigned)bus.bus, (unsigned)device_desc.device);
-    bus.dma_handle->unregister();
     free(pname);
 }
 

libraries/AP_HAL_ChibiOS/shared_dma.cpp

@@ -53,7 +53,6 @@ void Shared_DMA::unregister()
         locks[stream_id2].deallocate();
         locks[stream_id2].obj = nullptr;
     }
-    
 }
 
 // lock the DMA channels