ARM: zynq: remove incorrectly deleted file

My previous commit left the file empty and present in the
Makefile, which is a bit dirty and caused problems with
'make distclean', as pointed out by David Howells.
This hopefully cleans it up the right way.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: John Linn <john.linn@xilinx.com>

arch/arm/mach-zynq/Makefile

@@ -3,4 +3,4 @@
 #
 
 # Common support
-obj-y 				:= common.o timer.o board_dt.o
+obj-y				:= common.o timer.o