dma-mapping: fix direction in dma_alloc direction traces

Set __entry->dir to the actual "dir" parameter of all trace events
in dma_alloc_class. This struct member was left uninitialized by
mistake.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Fixes: 3afff779 ("dma-mapping: trace dma_alloc/free direction")
Cc: stable@vger.kernel.org
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20251001061028.412258-1-ptesarik@suse.com