riscv: bootstage: correct bootstage_report guard

Below warning can be occurred when CONFIG_BOOTSTAGE and
!CONFIG_SPL_BOOTSTAGE. It should be guarded by using CONFIG_IS_ENABLED
for SPL build.

arch/riscv/lib/bootm.c:46:9: warning: implicit declaration of
function 'bootstage_report'
   46 |         bootstage_report();
      |         ^~~~~~~~~~~~~~~~
      |         bootstage_error

Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/lib/bootm.c b/arch/riscv/lib/bootm.c
index 276677a..cc30efc 100644
--- a/arch/riscv/lib/bootm.c
+++ b/arch/riscv/lib/bootm.c
@@ -42,7 +42,7 @@
 #ifdef CONFIG_BOOTSTAGE_FDT
 	bootstage_fdt_add_report();
 #endif
-#ifdef CONFIG_BOOTSTAGE_REPORT
+#if CONFIG_IS_ENABLED(BOOTSTAGE_REPORT)
 	bootstage_report();
 #endif