Compile mmcv with custom op when not using cuda

[tangyanf]

When I compile mmcv with custom op on a machine that does not have cuda installed, I will encounter the following error：

So I modified the code to get the cuda header file path when compiling Ort custom op in setup.py

[codecov]

Codecov Report

Merging #945 (c1ff46c) into master (79f8cbd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #945   +/-   ##
=======================================
  Coverage   65.67%   65.67%           
=======================================
  Files         149      149           
  Lines        9451     9451           
  Branches     1720     1720           
=======================================
  Hits         6207     6207           
  Misses       2924     2924           
  Partials      320      320           

Flag	Coverage Δ
unittests	65.67% <ø> (ø)

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[zhouzaida]

LGTM