powerpc: Remove dead module_find_bug code

Doing some various "make randconfig", I came across an error when
CONFIG_BUG was not set:

arch/powerpc/kernel/module.c: In function 'module_find_bug':
arch/powerpc/kernel/module.c:111: error: increment of pointer to unknown structure
arch/powerpc/kernel/module.c:111: error: arithmetic on pointer to an incomplete type
arch/powerpc/kernel/module.c:112: error: dereferencing pointer to incomplete type

Looking further into this, I found that module_find_bug, defined in
powerpc arch code, is not called anywhere, so this just removes it.

There is a static module_find_bug in lib/bug.c but that is a separate issue.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>