target/mips: fix delay slot detection in gen_msa_branch()

It is unnecessary to test R6 from delay/forbidden slot check
in gen_msa_branch().

https://bugs.launchpad.net/qemu/+bug/1663287Reported-by: NBrian Campbell <bacam@z273.org.uk>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

target/mips/translate.c

@@ -18162,7 +18162,7 @@ static void gen_msa_branch(CPUMIPSState *env, DisasContext *ctx, uint32_t op1)
 
     check_msa_access(ctx);
 
-    if (ctx->insn_flags & ISA_MIPS32R6 && ctx->hflags & MIPS_HFLAG_BMASK) {
+    if (ctx->hflags & MIPS_HFLAG_BMASK) {
         generate_exception_end(ctx, EXCP_RI);
         return;
     }