serial: samsung: Use right device for DMA-mapping calls

Driver should provide its own struct device for all DMA-mapping calls instead
of extracting device pointer from DMA engine channel. Although this is harmless
from the driver operation perspective on ARM architecture, it is always good
to use the DMA mapping API in a proper way. This patch fixes following DMA API
debug warning:

WARNING: CPU: 0 PID: 0 at lib/dma-debug.c:1241 check_sync+0x520/0x9f4
samsung-uart 12c20000.serial: DMA-API: device driver tries to sync DMA memory it has not allocated [device address=0x000000006df0f580] [size=64 bytes]
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.11.0-rc1-00137-g07ca963 #51
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c011aaa4>] (unwind_backtrace) from [<c01127c0>] (show_stack+0x20/0x24)
[<c01127c0>] (show_stack) from [<c06ba5d8>] (dump_stack+0x84/0xa0)
[<c06ba5d8>] (dump_stack) from [<c0139528>] (__warn+0x14c/0x180)
[<c0139528>] (__warn) from [<c01395a4>] (warn_slowpath_fmt+0x48/0x50)
[<c01395a4>] (warn_slowpath_fmt) from [<c0729058>] (check_sync+0x520/0x9f4)
[<c0729058>] (check_sync) from [<c072967c>] (debug_dma_sync_single_for_device+0x88/0xc8)
[<c072967c>] (debug_dma_sync_single_for_device) from [<c0803c10>] (s3c24xx_serial_start_tx_dma+0x100/0x2f8)
[<c0803c10>] (s3c24xx_serial_start_tx_dma) from [<c0804338>] (s3c24xx_serial_tx_chars+0x198/0x33c)

Reported-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Fixes: 62c37eed ("serial: samsung: add dma reqest/release functions")
CC: stable@vger.kernel.org # v4.0+
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>