clk: zynqmp: Remove a unused variable

clk: zynqmp: Remove a unused variable

Fixes the following warning

drivers/clk/zynqmp/clkc.c:155:20: warning: 'usb0_mio_mux_parents'
defined but not used [-Wunused-variable]
static const char *usb0_mio_mux_parents[] __initconst = {usb0_bus_ref,
^
drivers/clk/zynqmp/clkc.c:157:20: warning: 'usb1_mio_mux_parents'
defined but not used [-Wunused-variable]
static const char *usb1_mio_mux_parents[] __initconst = {usb1_bus_ref,

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>