missing user_stack_pointer() instances

for the architectures that have usp in pt_regs and do not have
user_stack_pointer() already defined.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h
index cec5e12..a3186f2 100644
--- a/arch/mips/include/asm/ptrace.h
+++ b/arch/mips/include/asm/ptrace.h
@@ -49,6 +49,7 @@
 
 #define instruction_pointer(regs) ((regs)->cp0_epc)
 #define profile_pc(regs) instruction_pointer(regs)
+#define user_stack_pointer(r) ((r)->regs[29])
 
 extern asmlinkage void syscall_trace_enter(struct pt_regs *regs);
 extern asmlinkage void syscall_trace_leave(struct pt_regs *regs);