memory: brcmstb_dpfe: fix testing array offset after use

Code should first check for valid value of array offset, then use it as
the index.  Fixes smatch warning:

  drivers/memory/brcmstb_dpfe.c:443 __send_command() error: testing array offset 'cmd' after use.

Fixes: 2f330caff5 ("memory: brcmstb: Add driver for DPFE")
Acked-by: Markus Mayer <mmayer@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20230513112931.176066-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

drivers/memory/brcmstb_dpfe.c

@@ -434,15 +434,17 @@ static void __finalize_command(struct brcmstb_dpfe_priv *priv)
 static int __send_command(struct brcmstb_dpfe_priv *priv, unsigned int cmd,
 			  u32 result[])
 {
-	const u32 *msg = priv->dpfe_api->command[cmd];
 	void __iomem *regs = priv->regs;
 	unsigned int i, chksum, chksum_idx;
+	const u32 *msg;
 	int ret = 0;
 	u32 resp;
 
 	if (cmd >= DPFE_CMD_MAX)
 		return -1;
 
+	msg = priv->dpfe_api->command[cmd];
+
 	mutex_lock(&priv->lock);
 
 	/* Wait for DCPU to become ready */