drivers: dma: Remove unused function

Building with clang warns:

drivers/dma/dma_emul.c:73:20: error: unused function
'dma_emul_xfer_is_error_status' [-Werror,-Wunused-function]
static inline bool dma_emul_xfer_is_error_status(int status)
                   ^

Signed-off-by: Tom Hughes <tomhughes@chromium.org>

drivers/dma/dma_emul.c

@@ -70,11 +70,6 @@ static void dma_emul_work_handler(struct k_work *work);
 
 LOG_MODULE_REGISTER(dma_emul, CONFIG_DMA_LOG_LEVEL);
 
-static inline bool dma_emul_xfer_is_error_status(int status)
-{
-	return status < 0;
-}
-
 static inline const char *const dma_emul_channel_state_to_string(enum dma_emul_channel_state state)
 {
 	switch (state) {