zap_vma_ptes no longer returns an error code as of Linux's
27d036e33237e4 ("mm: Remove return value of zap_vma_ptes()"),
where they decided nobody is interested in it....
Just copy the check out of the function.
Change-Id: I2eda0f91ec55a34bba96f45cc3d887bc80132a82
Originally-by: Kagawa Kodai <fj1731iw@aa.jp.fujitsu.com>