powerpc/ftrace: Fix nop of modules on 64bit LE (ABIv2)

There is a bug in the handling of the function entry when we are nopping
out a branch from a module in ftrace.

We compare the result of module_trampoline_target() with the value of
ppc_function_entry(), and expect them to be true. But they never will
be.

module_trampoline_target() will always return the global entry point of
the function, whereas ppc_function_entry() will always return the local.

Fix it by using the newly added ppc_global_function_entry().

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>