vapi: remove directory name from include guards

vapi: remove directory name from include guards

Script vapi_c_gen.py uses full paths to source files to generate include
guards in files with `.vapi.h` extension. This makes the content of
header files depend on build directory which causes reproducibility
issues (cannot get identical build output when building in a different
directory).

Commit 4c64b6edc86f7 fixes this for .hpp files, but seems to forget
about .h files. Use its fix for these as well.

Type: fix
Change-Id: Ida638c7b4630fac1f6d968a9203a409648bef55c
Signed-off-by: Oleksandr Hnatiuk <[email protected]>