tracing, x86: function return tracer, fix assembly constraints

fix:

 arch/x86/kernel/ftrace.c: Assembler messages:
 arch/x86/kernel/ftrace.c:140: Error: missing ')'
 arch/x86/kernel/ftrace.c:140: Error: junk `(%ebp))' after expression
 arch/x86/kernel/ftrace.c:141: Error: missing ')'
 arch/x86/kernel/ftrace.c:141: Error: junk `(%ebp))' after expression

the [parent_replaced] is used in an =rm fashion, so that constraint
is correct in isolation - but [parent_old] aliases register %0 and uses
it in an addressing mode that is only valid with registers - so change
the constraint from =rm to =r.

This fixes the build failure.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/ftrace.c

@@ -151,7 +151,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 		"   .long 2b, 3b\n"
 		".previous\n"
 
-		: [parent_replaced] "=rm" (parent), [old] "=r" (old),
+		: [parent_replaced] "=r" (parent), [old] "=r" (old),
 		  [faulted] "=r" (faulted)
 		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
 		: "memory"