powerpc64/ftrace: fix module loading without patchable function entries

In the Linux kernel, the following vulnerability has been resolved:

powerpc64/ftrace: fix module loading without patchable function entries

get_stubs_size assumes that there must always be at least one patchable
function entry, which is not always the case (modules that export data
but no code), otherwise it returns -ENOEXEC and thus the section header
sh_size is set to that value. During module_memory_alloc() the size is
passed to execmem_alloc() after being page-aligned and thus set to zero
which will cause it to fail the allocation (and thus module loading) as
__vmalloc_node_range() checks for zero-sized allocs and returns null:

[ 115.466896] module_64: cast_common: doesn't contain __patchable_function_entries.
[ 115.469189] ------------[ cut here ]------------
[ 115.469496] WARNING: CPU: 0 PID: 274 at mm/vmalloc.c:3778 __vmalloc_node_range_noprof+0x8b4/0x8f0
...
[ 115.478574] ---[ end trace 0000000000000000 ]---
[ 115.479545] execmem: unable to allocate memory

Fix this by removing the check completely, since it is anyway not
helpful to propagate this as an error upwards.