HID: Intel-thc-hid: Intel-thc: fix dma_unmap_sg() nents value

HID: Intel-thc-hid: Intel-thc: fix dma_unmap_sg() nents value

The `dma_unmap_sg()` functions should be called with the same nents as the
`dma_map_sg()`, not the value the map function returned.

Save the number of entries in struct thc_dma_configuration.

Fixes: a688404b2e20 ("HID: intel-thc-hid: intel-thc: Add THC DMA interfaces")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Reviewed-by: Even Xu <even.xu@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>