RISC-V: Remove erroneous comment from translate.c

Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/translate.c

@@ -280,7 +280,6 @@ static void gen_arith(DisasContext *ctx, uint32_t opc, int rd, int rs1,
         tcg_gen_andi_tl(source2, source2, 0x1F);
         tcg_gen_sar_tl(source1, source1, source2);
         break;
-        /* fall through to SRA */
 #endif
     case OPC_RISC_SRA:
         tcg_gen_andi_tl(source2, source2, TARGET_LONG_BITS - 1);