powerpc/mm: flatten function __find_linux_pte() step 3

__find_linux_pte() is full of if/else which is hard to
follow allthough the handling is pretty simple.

Previous patches left a { } block. This patch removes it.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>