Renaming of cv.slet to cv.sle

Created by: MaryBennett

For issue #100

Files Changes:

• gas/testsuite/gas/riscv/cv-alu-slet.d: Changed the name of cv.slet.
• gas/testsuite/gas/riscv/cv-alu-sletu.d: Likewise.
• opcodes/riscv-opc.c: Likewise.