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>

arch/m32r/include/asm/ptrace.h

@@ -134,6 +134,7 @@ extern void init_debug_traps(struct task_struct *);
 
 #define instruction_pointer(regs) ((regs)->bpc)
 #define profile_pc(regs) instruction_pointer(regs)
+#define user_stack_pointer(regs) ((regs)->spu)
 
 extern void withdraw_debug_trap(struct pt_regs *regs);