fpga: Use tab instead of space indentation

In FPGA Makefile has both space and tab indentation, to
make them align use tab instead of space indentation.
Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Link: https://lore.kernel.org/r/20220423170235.2115479-5-nava.manne@xilinx.comSigned-off-by: Xu Yilun <yilun.xu@intel.com>