x86/ia32_signal: Propagate __user annotation properly

x86/ia32_signal: Propagate __user annotation properly

Commit

  57d563c82925 ("x86: ia32_setup_rt_frame(): consolidate uaccess areas")

dropped a __user annotation in a cast when refactoring __put_user() to
unsafe_put_user().

Hence, since then, sparse warns in arch/x86/ia32/ia32_signal.c:350:9:

  warning: cast removes address space '__user' of expression
  warning: incorrect type in argument 1 (different address spaces)
    expected void const volatile [noderef] __user *ptr
    got unsigned long long [usertype] *

Add the __user annotation to restore the propagation of address spaces.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201207124141.21859-1-lukas.bulwahn@gmail.com