module: fix BUG_ON() for powerpc (and other function descriptor archs)

The rarely-used symbol_put_addr() needs to use dereference_function_descriptor
on powerpc.

Reported-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au.>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>