x86/pkeys/selftests: Rename 'si_pkey' to 'siginfo_pkey'

x86/pkeys/selftests: Rename 'si_pkey' to 'siginfo_pkey'

'si_pkey' is now #defined to be the name of the new siginfo field that
protection keys uses.  Rename it not to conflict.

Signed-off-by: Dave Hansen <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>