engicam: imx6q: Return mmc dev 0 for icore

icorem6 has sd on usdhci1 which is devno 0 so return proper
devno from board_mmc_get_env_dev for icorem6 and icorem_6rqs

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/board/engicam/imx6q/imx6q.c b/board/engicam/imx6q/imx6q.c
index bb0c866..fe37088 100644
--- a/board/engicam/imx6q/imx6q.c
+++ b/board/engicam/imx6q/imx6q.c
@@ -193,6 +193,7 @@
 #ifdef CONFIG_ENV_IS_IN_MMC
 int board_mmc_get_env_dev(int devno)
 {
-	return devno - 1;
+	/* i.CoreM6 RQS has USDHC3 for SD and USDHC4 for eMMC */
+	return (devno == 0) ? 0: (devno - 1);
 }
 #endif