powerpc: fix building hvc_opal.c

Fix building following build error:

  drivers/tty/hvc/hvc_opal.c:244:12: error: 'THIS_MODULE' undeclared here (not in a function)

Signed-off-by: Michael Neuling <mikey@neuling.org>
[ New file from powerpc tree not following the new rules from the
  module.h split, both of which were merged today.  - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>