[scudo] Fix implicitly narrow casting (NFC)

u16 may be promoted to int by arithmetic type conversion. Do an explicit
cast to avoid certain compiler's warning. This fixes the problem
introduced by 0fb2aeef5310eaba2915b30810464a744a80da15

Differential Revision: https://reviews.llvm.org/D135985

GitOrigin-RevId: 3ead26e65bab612e6aead979646b40c6c15d9ba6
1 file changed