x86/irq: Fix undefined behaviour in irq_move_cleanup_interrupt()

x86/irq: Fix undefined behaviour in irq_move_cleanup_interrupt()

UBSAN reports:

  (XEN) ================================================================================
  (XEN) UBSAN: Undefined behaviour in irq.c:682:22
  (XEN) left shift of 1 by 31 places cannot be represented in type 'int'
  (XEN) ----[ Xen-4.13-unstable  x86_64  debug=y   Not tainted ]----
  (XEN) CPU:    16
  (XEN) RIP:    e008:[<ffff82d0802a54ce>] ubsan.c#ubsan_epilogue+0xa/0xc2
  <snip>
  (XEN) Xen call trace:
  (XEN)    [<ffff82d0802a54ce>] ubsan.c#ubsan_epilogue+0xa/0xc2
  (XEN)    [<ffff82d0802a6009>] __ubsan_handle_shift_out_of_bounds+0x15d/0x16c
  (XEN)    [<ffff82d08031ae77>] irq_move_cleanup_interrupt+0x25c/0x4a0
  (XEN)    [<ffff82d08031b585>] do_IRQ+0x19d/0x104c
  (XEN)    [<ffff82d08050c8ba>] common_interrupt+0x10a/0x120
  (XEN)    [<ffff82d0803b13a6>] cpu_idle.c#acpi_idle_do_entry+0x1de/0x24b
  (XEN)    [<ffff82d0803b1d83>] cpu_idle.c#acpi_processor_idle+0x5c8/0x94e
  (XEN)    [<ffff82d0802fa8d6>] domain.c#idle_loop+0xee/0x101
  (XEN)
  (XEN) ================================================================================

Switch to an unsigned shift, and correct the surrounding style.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>