selftests/thermal: remove duplicate sprintf() call in workload_hint_test

Remove redundant sprintf() call that was duplicating the same operation of
formatting delay_str with argv[1].

Link: https://lkml.kernel.org/r/6338CD0E839B770B+20250710130412.284531-1-wangyuli@uniontech.com


Signed-off-by: WangYuli <wangyuli@uniontech.com>
Cc: Guan Wentao <guanwentao@uniontech.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>