[NFC] Use the same type for bit fields in MCSchedClassDesc

Otherwise they are not allocated as a single bit field and take 4
bytes instead of 2.

Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D95954

GitOrigin-RevId: 4bee0dc918d20a52be9d1766c82a642268b5e1ee
1 file changed