powerpc/process: Remove unnecessary #ifdef CONFIG_FUNCTION_GRAPH_TRACER

ftrace_graph_ret_addr() is always defined and returns 'ip' when
CONFIG_FUNCTION GRAPH_TRACER is not set.

So the #ifdef is not needed, remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/9d11143d4e27ba8274369a926968756917584868.1597643153.git.christophe.leroy@csgroup.eu