powerpc/ftrace: Fix printf format warning

'tramp' is an unsigned long, so print it with %lx.

Fixes the following build warning:
arch/powerpc/kernel/ftrace.c:291: error: format ‘%x’ expects type ‘unsigned int’, but argument 2 has type ‘long unsigned int’

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>