ARM: tegra: remove redundant mkdirs from board Makefiles

None of harmony, seaboard, ventana, whistler directly build files from
../common/, so there's no need to mkdir the obj directory for such files.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/board/nvidia/ventana/Makefile b/board/nvidia/ventana/Makefile
index e3b7435..611520c 100644
--- a/board/nvidia/ventana/Makefile
+++ b/board/nvidia/ventana/Makefile
@@ -25,7 +25,7 @@
 include $(TOPDIR)/config.mk
 
 ifneq ($(OBJTREE),$(SRCTREE))
-$(shell mkdir -p $(obj)../common $(obj)../seaboard)
+$(shell mkdir -p $(obj)../seaboard)
 endif
 
 LIB	= $(obj)lib$(BOARD).o