tests: timer_api: unused var when CONFIG_ZTEST_ASSERT_VERBOSE=0

When CONFIG_ZTEST_ASSERT_VERBOSE is 0, the array round_s is not
being used by zassert_true(). So mark it __maybe_unused to
avoid compiler warnings.

Signed-off-by: Daniel Leung <[email protected]>

Author: dcpleung

tests/kernel/timer/timer_api/src/timer_convert.c

@@ -14,7 +14,7 @@ enum units { UNIT_ticks, UNIT_cyc, UNIT_ms, UNIT_us, UNIT_ns };
 
 enum round { ROUND_floor, ROUND_ceil, ROUND_near };
 
-static const char *const round_s[] = {
+static const char *const round_s[] __maybe_unused = {
 	[ROUND_floor] = "floor",
 	[ROUND_ceil] = "ceil",
 	[ROUND_near] = "near",