fuzz/x86_emulate: actually use cpu_regs input

fuzz/x86_emulate: actually use cpu_regs input

Commit c07574b reorganized the way fuzzing was done, explicitly
creating a structure that the input data would be copied into.

Unfortunately, the cpu register state used by the emulator is on the
stack; it's cleared, but data is never copied into it.

If we're explicitly setting an entirely new cpu_regs struct for each
new input anyway, there's no need to have two copies around anymore;
just point to the one in the data structure.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>