powerpc/ptdump: Fix W+X verification call in mark_rodata_ro()

ptdump_check_wx() also have to be called when pages are mapped
by blocks.

Fixes: 453d87f6

 ("powerpc/mm: Warn if W+X pages found on boot")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/37517da8310f4457f28921a4edb88fb21d27b62a.1578989531.git.christophe.leroy@c-s.fr