vkbench: Make fmt::formatter<FilePath>::format const

Fixes this build error:

/usr/include/fmt/base.h:1402:29: error: passing `const fmt::v11::formatter<FilePath>` as `this` argument discards qualifiers [-fpermissive]
 1402 |     ctx.advance_to(cf.format(*static_cast<qualified_type*>(arg), ctx));
      |                     ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /scratch/vkbench-git/src/vkbench/src/utils.h:21:
/scratch/vkbench-git/src/vkbench/src/filepath.h:37:8: note:   in call to `auto fmt::v11::formatter<FilePath>::format(FilePath, FormatContext&) [with FormatContext = fmt::v11::context]`
   37 |   auto format(FilePath c, FormatContext& ctx) {
      |        ^~~~~~

BUG=b:368394746
TEST=Build Borealis

Change-Id: I618a4258bf88595d0d5bf46b9829f2e5ac46e00c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vkbench/+/5876375
Commit-Queue: Ilja Friedel <[email protected]>
Reviewed-by: Ilja Friedel <[email protected]>
Tested-by: Phillip Pearson <[email protected]>
Auto-Submit: Phillip Pearson <[email protected]>
1 file changed