CRED: Wrap task credential accesses in the PA-RISC arch

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Kyle McMartin <kyle@mcmartin.ca>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Grant Grundler <grundler@parisc-linux.org>
Cc: linux-parisc@vger.kernel.org
Signed-off-by: James Morris <jmorris@namei.org>

arch/parisc/kernel/signal.c

@@ -182,7 +182,7 @@ sys_rt_sigreturn(struct pt_regs *regs, int in_syscall)
 	si.si_errno = 0;
 	si.si_code = SI_KERNEL;
 	si.si_pid = task_pid_vnr(current);
-	si.si_uid = current->uid;
+	si.si_uid = current_uid();
 	si.si_addr = &frame->uc;
 	force_sig_info(SIGSEGV, &si, current);
 	return;