tools/insn-fuzz: Fix a stability bug in afl-clang-fast mode

tools/insn-fuzz: Fix a stability bug in afl-clang-fast mode

The fuzzing harness conditionally disables hooks to test error paths in the
emulator.  However, fuzz_emulops is a static structure.

c/s 69f4633 "tools/insn-fuzz: Support AFL's afl-clang-fast mode" introduced
persistent mode, but because fuzz_emulops is static, the clobbering of hooks
accumulates over repeated input, meaning that previous corpora influence the
execution over the current corpus.

Move the partially clobbered struct x86_emulate_ops into struct fuzz_state,
which is re-initialised from full on each call to LLVMFuzzerTestOneInput()

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>