dmaengine: stm32-mdma: Remove dead code in stm32_mdma_irq_handler()

Local variable chan is initialized by an address of element of chan array
that is part of stm32_mdma_device struct, so it does not make sense to
compare chan with NULL.

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: NAlexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: a4ffb13c ("dmaengine: Add STM32 MDMA driver")
Reviewed-by: NAmelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/1655072638-9103-1-git-send-email-khoroshilov@ispras.ruSigned-off-by: NVinod Koul <vkoul@kernel.org>

drivers/dma/stm32-mdma.c

@@ -1328,12 +1328,7 @@ static irqreturn_t stm32_mdma_irq_handler(int irq, void *devid)
 		return IRQ_NONE;
 	}
 	id = __ffs(status);
-
 	chan = &dmadev->chan[id];
-	if (!chan) {
-		dev_warn(mdma2dev(dmadev), "MDMA channel not initialized\n");
-		return IRQ_NONE;
-	}
 
 	/* Handle interrupt for the channel */
 	spin_lock(&chan->vchan.lock);