imx: spl: Fix use of removed SPL_FAT_SUPPORT config

CONFIG_SPL_FAT_SUPPORT was removed in commit 0c3a9ed409a5
("spl: Kconfig: Replace CONFIG_SPL_FAT_SUPPORT with CONFIG_SPL_FS_FAT").
Fixup a leftover use of the symbol.

Fixes: 9d86dbd9cf9d ("imx: spl: implement spl_boot_mode for i.MX7/8/8M")
Signed-off-by: Harald Seiler <hws@denx.de>
diff --git a/arch/arm/mach-imx/spl.c b/arch/arm/mach-imx/spl.c
index 32d78b7..fd3fa04 100644
--- a/arch/arm/mach-imx/spl.c
+++ b/arch/arm/mach-imx/spl.c
@@ -197,14 +197,14 @@
 	case SD1_BOOT:
 	case SD2_BOOT:
 	case SD3_BOOT:
-		if (IS_ENABLED(CONFIG_SPL_FAT_SUPPORT))
+		if (IS_ENABLED(CONFIG_SPL_FS_FAT))
 			return MMCSD_MODE_FS;
 		else
 			return MMCSD_MODE_RAW;
 	case MMC1_BOOT:
 	case MMC2_BOOT:
 	case MMC3_BOOT:
-		if (IS_ENABLED(CONFIG_SPL_FAT_SUPPORT))
+		if (IS_ENABLED(CONFIG_SPL_FS_FAT))
 			return MMCSD_MODE_FS;
 		else if (IS_ENABLED(CONFIG_SUPPORT_EMMC_BOOT))
 			return MMCSD_MODE_EMMCBOOT;