ioprio: allow sys_ioprio_set() value of 0 to reset ioprio setting
ioprio: allow sys_ioprio_set() value of 0 to reset ioprio setting

Normally io priorities follow the CPU nice, unless a specific scheduling
class has been set. Once that is set, there's no way to reset the
behaviour to 'none' so that it follows CPU nice again.

Currently passing in 0 as the ioprio class/value will return -1/EINVAL,
change that to allow resetting of a set scheduling class.

Signed-off-by: Jens Axboe <165ab144a3ccfd9429d5c6466b275f24fafdb114@oracle.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs