Fix missing slash in fpga codegen

[manuelburger]

While compiling and running on Xilinx FPGA I ran into the following issue:

terminate called after throwing an instance of 'hlslib::ocl::ConfigurationError'
  what():  Failed to open program file "/home/burgerm/thesis_dace/tasks/blas/level1/axpy/.dacecache/saxpy_perf/buildsaxpy_perf_hw.xclbin".

There is a / missing between ...build and $PROGRAM_NAME .The small change should fix it.

[codecov]

Codecov Report

Merging #175 into master will decrease coverage by 0.50%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #175      +/-   ##
==========================================
- Coverage   76.93%   76.43%   -0.50%     
==========================================
  Files         112      112              
  Lines       24347    24347              
==========================================
- Hits        18731    18609     -122     
- Misses       5616     5738     +122     

Impacted Files	Coverage Δ
dace/codegen/targets/xilinx.py	92.06% <100.00%> (ø)
dace/transformation/dataflow/copy_to_device.py	26.80% <0.00%> (-67.01%)	⬇️
...ce/transformation/interstate/gpu_transform_sdfg.py	77.25% <0.00%> (-12.57%)	⬇️
dace/transformation/dataflow/map_fission.py	89.71% <0.00%> (-1.65%)	⬇️
dace/transformation/dataflow/merge_arrays.py	95.08% <0.00%> (-1.64%)	⬇️
dace/codegen/targets/cpu.py	86.84% <0.00%> (-1.63%)	⬇️
dace/subsets.py	83.26% <0.00%> (-1.38%)	⬇️
dace/data.py	68.45% <0.00%> (-0.95%)	⬇️
dace/codegen/targets/cuda.py	84.38% <0.00%> (-0.84%)	⬇️
...sformation/dataflow/gpu_transform_local_storage.py	85.37% <0.00%> (-0.30%)	⬇️
... and 1 more

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[definelicht]

@manuelburger I see Tiziano did this fix for Intel also, we just didn't carry it over to Xilinx. Could you put the slash inside the string please, then I'll approve:

kernel_file_name = "DACE_BINARY_DIR \"/{}".format(self._program_name)