Makefile: specifiy an explicite object name rather than $(BOARD).o

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/board/ti/beagle/Makefile b/board/ti/beagle/Makefile
index 9f55e8f..7a858be 100644
--- a/board/ti/beagle/Makefile
+++ b/board/ti/beagle/Makefile
@@ -5,5 +5,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y	:= $(BOARD).o
+obj-y	:= beagle.o
 obj-$(CONFIG_STATUS_LED) += led.o