arm: Tegra: Fix Harmony and Ventana builds in u-boot-tegra/master

Seaboard changes have removed the need for common/board.o in the
Makefile. Propagate this change to the other Tegra2 builds.

Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/board/nvidia/ventana/Makefile b/board/nvidia/ventana/Makefile
index d5140c8..eced323 100644
--- a/board/nvidia/ventana/Makefile
+++ b/board/nvidia/ventana/Makefile
@@ -31,8 +31,7 @@
 
 LIB	= $(obj)lib$(BOARD).o
 
-COBJS	+= ../seaboard/seaboard.o
-COBJS	+= ../common/board.o
+COBJS	= ../seaboard/seaboard.o
 
 SRCS	:= $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))