[ia64] access_uarea(): stop bothering with gpregs_[gs]et()

We know this won't be called for child == current, so we don't need
to bother with callbacks, etc. - just do unw_init_from_blocked_task(),
unw_unwind_to_user() and do the payload of gpregs_[gs]et().  For
one register.  Which is to say, access_elf_reg().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/ia64/kernel/ptrace.c

@@ -1936,15 +1936,14 @@ access_uarea(struct task_struct *child, unsigned long addr,
 	}
 
 	if (pos != -1) {
-		if (write_access)
-			ret = gpregs_set(child, NULL, pos,
-				sizeof(unsigned long), data, NULL);
-		else
-			ret = gpregs_get(child, NULL, pos,
-				sizeof(unsigned long), data, NULL);
-		if (ret != 0)
-			return -1;
+		struct unw_frame_info info;
+
+		memset(&info, 0, sizeof(info));
+		unw_init_from_blocked_task(&info, child);
+		if (unw_unwind_to_user(&info) < 0)
 			return 0;
+
+		return access_elf_reg(child, &info, pos, data, write_access);
 	}
 
 	/* access debug registers */