[backends] fix warnings introduced in PR #645

[tdavidcl]

No description provided.

[github-actions]

Pre-commit check: ✅

trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check for merge conflicts................................................Passed
check that executables have shebangs.....................................Passed
check that scripts with shebangs are executable..........................Passed
check for added large files..............................................Passed
check for case conflicts.................................................Passed
check yaml...............................................................Passed
detect private key.......................................................Passed
Validate GitHub Workflows................................................Passed
clang-format.............................................................Passed
Check doxygen headers....................................................Passed
Check license headers....................................................Passed
Check #pragma once.......................................................Passed
Check SYCL #include......................................................Passed

Test pipeline can run.

[github-actions]

Doxygen diff with main

Removed warnings : 0
New warnings : 0
Warnings count : 5586 → 5586 (0.0%)

Detailed changes :