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 <lkp@intel.com>
Fixes: d9650682 ("dmaengine: PTDMA: support polled mode")
Link: https://lore.kernel.org/r/20220421052407.745637-1-vkoul@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>