Remove -add from xdc files

Signed-off-by: Anton Blanchard <anton@linux.ibm.com>

fpga/arty_a7.xdc

@@ -531,7 +531,7 @@ set_property CONFIG_MODE SPIx4 [current_design]
 # Clock constraints
 ################################################################################
 
-create_clock -add -name sys_clk_pin -period 10.00 [get_ports { ext_clk }];
+create_clock -name sys_clk_pin -period 10.00 [get_ports { ext_clk }];
 
 create_clock -name eth_rx_clk -period 40.0 [get_ports { eth_clocks_rx }]
 

fpga/cmod_a7-35.xdc

@@ -1,6 +1,6 @@
 ## Clock signal 12 MHz
 set_property -dict { PACKAGE_PIN L17   IOSTANDARD LVCMOS33 } [get_ports { ext_clk }];
-create_clock -add -name sys_clk_pin -period 83.33 [get_ports {ext_clk}];
+create_clock -name sys_clk_pin -period 83.33 [get_ports {ext_clk}];
 
 set_property -dict { PACKAGE_PIN J18   IOSTANDARD LVCMOS33 } [get_ports { uart0_txd }];
 set_property -dict { PACKAGE_PIN J17   IOSTANDARD LVCMOS33 } [get_ports { uart0_rxd  }];

fpga/nexys-video.xdc

@@ -313,7 +313,7 @@ set_property CONFIG_MODE SPIx4 [current_design]
 # Clock constraints
 ################################################################################
 
-create_clock -add -name sys_clk_pin -period 10.00 [get_ports { ext_clk }];
+create_clock -name sys_clk_pin -period 10.00 [get_ports { ext_clk }];
 
 ################################################################################
 # False path constraints (from LiteX as they relate to LiteDRAM)

fpga/nexys_a7.xdc

@@ -1,5 +1,5 @@
 set_property -dict {PACKAGE_PIN E3 IOSTANDARD LVCMOS33} [get_ports ext_clk]
-create_clock -period 10.000 -name sys_clk_pin -add [get_ports ext_clk]
+create_clock -period 10.000 -name sys_clk_pin [get_ports ext_clk]
 
 set_property -dict {PACKAGE_PIN C12 IOSTANDARD LVCMOS33} [get_ports ext_rst]