imx: imx8mp_rsb3720a1: fix incorrect ifdef check on SPL_MMC

Since commit 103c5f180694 ("mmc: Rename MMC_SUPPORT to MMC"),
SPL_MMC_SUPPORT is named SPL_MMC, so let's fix the ifdef.

Fixes: fbc6b1414342 ("imx: imx8mp_rsb3720a1: convert to DM_SERIAL")
Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
diff --git a/board/advantech/imx8mp_rsb3720a1/imx8mp_rsb3720a1.c b/board/advantech/imx8mp_rsb3720a1/imx8mp_rsb3720a1.c
index 0a1b2c9..aa9687f 100644
--- a/board/advantech/imx8mp_rsb3720a1/imx8mp_rsb3720a1.c
+++ b/board/advantech/imx8mp_rsb3720a1/imx8mp_rsb3720a1.c
@@ -206,7 +206,7 @@
 	return 0;
 }
 
-#ifdef CONFIG_SPL_MMC_SUPPORT
+#ifdef CONFIG_SPL_MMC
 #define UBOOT_RAW_SECTOR_OFFSET 0x40
 unsigned long spl_mmc_get_uboot_raw_sector(struct mmc *mmc)
 {
@@ -219,4 +219,4 @@
 		return CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR;
 	}
 }
-#endif /* CONFIG_SPL_MMC_SUPPORT */
+#endif /* CONFIG_SPL_MMC */