staging: clocking-wizard: Rename speed-grade to xlnx,speed-grade

Rename speed-grade to xlnx,speed-grade

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Link: https://lore.kernel.org/r/1614172241-17326-3-git-send-email-shubhrajyoti.datta@xilinx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>