This silences -Wmissing-prototypes when defining p9_release_pages.

Link: http://lkml.kernel.org/r/b1c4df8f21689b10d451c28fe38e860722d20e71.1542089696.git.dato@net.com.org.esSigned-off-by: NAdeodato Simó <dato@net.com.org.es>
Signed-off-by: NDominique Martinet <dominique.martinet@cea.fr>