cyclic: doc: Update documentation for CONFIG_CYCLIC_MAX_CPU_TIME_US

Cyclic now just print a warning once instead of disabling the cyclic
function when the cyclic function upon exceeding CPU time usage.

Fixes: ddc8d36a ("cyclic: Don't disable cylic function upon exceeding CPU time")
Signed-off-by: Weizhao Ouyang <o451686892@gmail.com>

Rephrase the paragraph.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>