dmaengine: sdxi: context: Allocate sizeof(*ptr), not sizeof(struct ...)

Remove the superfluous comment while we're at it.

Per upstream:
https://lore.kernel.org/dmaengine/20250915151257.0000253b@huawei.com/

SWLSVROS-5624

Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>

Author: nathanlynch

drivers/dma/sdxi/context.c

@@ -328,8 +328,7 @@ static struct sdxi_cxt *alloc_cxt(struct sdxi_dev *sdxi, bool privileged)
 	if (id == sdxi->max_cxts)
 		return NULL;
 
-	/* alloc context and initialize it */
-	cxt = kzalloc(sizeof(struct sdxi_cxt), GFP_KERNEL);
+	cxt = kzalloc(sizeof(*cxt), GFP_KERNEL);
 	if (!cxt)
 		return NULL;