[RISCV] Fix isel pattern of masked vmslt[u]

This patch changes the operand order of masked vmslt[u]
from (mask, rs1, scalar, maskedoff, vl)
to (maskedoff, rs1, scalar, mask, vl).

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D98839

(cherry picked from commit fca5d63a)