sys: refine EVIOCGMASK description
sys: refine EVIOCGMASK description

Fuzzer used this call to corrupt output data involving
treating part of file name as a pointer into data section.
Machines are raising...

google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,hyz0906/syzkaller,zoulasc/syzkaller,dotweiba/syzkaller,hyz0906/syzkaller,xairy/syzkaller,zoulasc/syzkaller,zoulasc/syzkaller,hyz0906/syzkaller,google/syzkaller,xairy/syzkaller,hyz0906/syzkaller,dotweiba/syzkaller,zoulasc/syzkaller,dotweiba/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,dotweiba/syzkaller,google/syzkaller,xairy/syzkaller,hyz0906/syzkaller,xairy/syzkaller,google/syzkaller