modify the return value according to posix standard
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SCHED_GET_PRIORITY_MAX(2)
NAME
sched_get_priority_max, sched_get_priority_min - get static priority range
RETURN VALUE
On success, sched_get_priority_max() and sched_get_priority_min() return the
maximum/minimum priority value for the named scheduling policy.
On error, -1 is returned, and errno is set appropriately.
ERRORS
EINVAL The argument policy does not identify a defined scheduling policy.
Signed-off-by: chao an <anchao@xiaomi.com>
1550747400