pch_uart: Fix dma_sync_sg_for_device() nents value

pch_uart: Fix dma_sync_sg_for_device() nents value

The dma_sync_sg_for_device() functions should be called with the same
nents as the dma_map_sg(), not the value the map function returned
according to the documentation in Documentation/core-api/dma-api.rst:450:
	With the sync_sg API, all the parameters must be the same
	as those passed into the sg mapping API.

Fixes: da3564ee027e ("pch_uart: add multi-scatter processing")
Cc: stable <stable@kernel.org>
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250701113452.18590-2-fourier.thomas@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>