dmaengine: ptdma: statify pt_tx_status

LKP bot reports a new warning:
Warning:
drivers/dma/ptdma/ptdma-dmaengine.c:262:1: warning: no previous prototype for 'pt_tx_status' [-Wmissing-prototypes]

pt_tx_status() should be static, so declare as such.

Reported-by: kernel test robot <[e-mail]>
Fixes: d965068259d1 ("dmaengine: PTDMA: support polled mode")
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/ptdma/ptdma-dmaengine.c

···
 		pt_cmd_callback(desc, 0);
 }
 
-enum dma_status
+static enum dma_status
 pt_tx_status(struct dma_chan *c, dma_cookie_t cookie,
 		struct dma_tx_state *txstate)
 {