freescale: p1_p2_rdb_pc: rename COBJS-y to obj-y

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/board/freescale/p1_p2_rdb_pc/Makefile b/board/freescale/p1_p2_rdb_pc/Makefile
index 8e20073..a2a1f92 100644
--- a/board/freescale/p1_p2_rdb_pc/Makefile
+++ b/board/freescale/p1_p2_rdb_pc/Makefile
@@ -18,7 +18,7 @@
 
 else
 ifdef CONFIG_SPL_BUILD
-COBJS-y += spl.o
+obj-y += spl.o
 endif
 
 obj-y        += p1_p2_rdb_pc.o