defines: prevent redefinition of UNUSED

To prevent compiler warnings/errors we have to wrap the definition of
UNUSED with an ifndef. So there are no problems if this is already
defined in the project

(cherry picked from commit 041404b9128b7117164508cc98c03c06818da315)

Original-Signed-off-by: Peter Tönz <[email protected]>
GitOrigin-RevId: 041404b9128b7117164508cc98c03c06818da315
Change-Id: Ie7cf80598567d8242bb2c6e7517ebdd2d3be2313
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/hal_stm32/+/3963658
Reviewed-by: Al Semjonovs <[email protected]>
Tested-by: Al Semjonovs <[email protected]>
Tested-by: CopyBot Service Account <[email protected]>
Commit-Queue: Al Semjonovs <[email protected]>
32 files changed