dm: core: Correct reference to DM_SPL in SPL_DM_STATS

This does not existing anymore. Update SPL_DM_STATS to use the correct
Kconfig option, which is SPL_DM

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/Kconfig b/drivers/core/Kconfig
index fe5c41d..209d90e 100644
--- a/drivers/core/Kconfig
+++ b/drivers/core/Kconfig
@@ -88,7 +88,7 @@
 
 config SPL_DM_STATS
 	bool "Collect and show driver model stats in SPL"
-	depends on DM_SPL
+	depends on SPL_DM
 	help
 	  Enable this to collect and display memory statistics about driver
 	  model. This can help to figure out where all the memory is going and