Correct SPL use of AHCI

This converts 1 usage of this option to the non-SPL form, since there is
no SPL_AHCI defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/compulab/cm_fx6/cm_fx6.c b/board/compulab/cm_fx6/cm_fx6.c
index 847ac33..7bce09e 100644
--- a/board/compulab/cm_fx6/cm_fx6.c
+++ b/board/compulab/cm_fx6/cm_fx6.c
@@ -736,7 +736,7 @@
 	.plat = &cm_fx6_mxc_serial_plat,
 };
 
-#if CONFIG_IS_ENABLED(AHCI)
+#if IS_ENABLED(CONFIG_AHCI)
 static int sata_imx_probe(struct udevice *dev)
 {
 	int i, err;