x86/shstk: Change order of __user in type

x86/shstk: Change order of __user in type

0day reports a sparse warning:
arch/x86/kernel/shstk.c:295:55: sparse: sparse: cast removes address space
'__user' of expression

The __user is in the wrong spot. Move it to right spot and make sparse
happy.

Closes: https://lore.kernel.org/oe-kbuild-all/202308222312.Jt4Tog5T-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20230825014554.1769194-1-rick.p.edgecombe%40intel.com