plugins: Assert mmu_idx in range before use in qemu_plugin_get_hwaddr

Coverity reports out-of-bound accesses here.  This should be a
false positive due to how the index is decoded from MemOpIdx.

Fixes: Coverity CID 1487201
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Damien Hedde <damien.hedde@greensocs.com>
Message-Id: <20220401190233.329360-1-richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220929114231.583801-37-alex.bennee@linaro.org>

plugins/api.c

@@ -289,6 +289,8 @@ struct qemu_plugin_hwaddr *qemu_plugin_get_hwaddr(qemu_plugin_meminfo_t info,
     enum qemu_plugin_mem_rw rw = get_plugin_meminfo_rw(info);
     hwaddr_info.is_store = (rw & QEMU_PLUGIN_MEM_W) != 0;
 
+    assert(mmu_idx < NB_MMU_MODES);
+
     if (!tlb_plugin_lookup(cpu, vaddr, mmu_idx,
                            hwaddr_info.is_store, &hwaddr_info)) {
         error_report("invalid use of qemu_plugin_get_hwaddr");