powerpc/ftrace: Replace use of ftrace_call_replace() with ftrace_create_branch_inst()

ftrace_create_branch_inst() is clearer about its intent than
ftrace_call_replace().

Signed-off-by: Naveen N Rao <naveen@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/953513b88fa922ba7a66d772dc1310710efe9177.1687166935.git.naveen@kernel.org