x86: show correct code in CPU state

x86: show correct code in CPU state

When showing the CPU state (e.g., after a crash) the dump of code
around RIP is incorrect.

Incorrect:

    Xen code around <ffff82d0801113cf> (...):
     00 c6 c1 ee 08 48 c1 e0 <04> 03 04 f1 8b ...
     ^^ Uninitialized         ^^ Missing 0x48

Correct:

    Xen code around <ffff82d0801113cf> (...):
     c6 c1 ee 08 48 c1 e0 04 <48> 03 04 f1 8b ...

When coping the bytes before RIP, the destination was off-by-one.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>