target/riscv: Fix vcompress with rvv_ta_all_1s

vcompress packs vl or less fields into vd, so the tail starts after the
last packed field. This could be more clearly expressed in the ISA,
but for now this thread helps to explain it:

https://github.com/riscv/riscv-v-spec/issues/796

Signed-off-by: Anton Blanchard <antonb@tenstorrent.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241030043538.939712-1-antonb@tenstorrent.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/vector_helper.c

@@ -5132,7 +5132,7 @@ void HELPER(NAME)(void *vd, void *v0, void *vs1, void *vs2,               \
     }                                                                     \
     env->vstart = 0;                                                      \
     /* set tail elements to 1s */                                         \
-    vext_set_elems_1s(vd, vta, vl * esz, total_elems * esz);              \
+    vext_set_elems_1s(vd, vta, num * esz, total_elems * esz);             \
 }
 
 /* Compress into vd elements of vs2 where vs1 is enabled */