Fix logic errors on _backend identification.

[lhartmann]

I got the compile error below, and went to check the sources. Turns out there was a logic error on backed type detection. Just patched the code following the pattern on the rest of the file.

IMHO that many switch(...) inside a class feels dirty. Maybe refactor backends as a separate classes?

/tmp/openFPGALoader/src/cmsisDAP.cpp: In constructor ‘CmsisDAP::CmsisDAP(const cable_t&, int, uint32_t, int8_t)’:
/tmp/openFPGALoader/src/cmsisDAP.cpp:204:35: error: ‘_hid_dev’ was not declared in this scope
  204 |                         hid_close(_hid_dev);
      |                                   ^~~~~~~~
/tmp/openFPGALoader/src/cmsisDAP.cpp:204:25: error: ‘hid_close’ was not declared in this scope
  204 |                         hid_close(_hid_dev);
      |                         ^~~~~~~~~
/tmp/openFPGALoader/src/cmsisDAP.cpp:205:25: error: ‘hid_exit’ was not declared in this scope
  205 |                         hid_exit();
      |                         ^~~~~~~~

[trabucayre]

Good catch!
Applied
Thanks @lhartmann !