storage: fix the error message when encrypted raw volume resize
storage: fix the error message when encrypted raw volume resize

The vol-dumpxml shows the volume target format type as raw for
encrypted volumes. The error message when attempting to resize
with prealloc is confusing here.

Signed-off-by: Shivaprasad G Bhat <90f736271cc61454bf7410f17f3d154578105aa0@linux.vnet.ibm.com>
Reviewed-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

andreabolognani/libvirt,jfehlig/libvirt,jardasgit/libvirt,libvirt/libvirt,libvirt/libvirt,jardasgit/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,crobinso/libvirt,fabianfreyer/libvirt,crobinso/libvirt,olafhering/libvirt,jardasgit/libvirt,jardasgit/libvirt,andreabolognani/libvirt,eskultety/libvirt,zippy2/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,eskultety/libvirt,andreabolognani/libvirt,jfehlig/libvirt,nertpinx/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,eskultety/libvirt,zippy2/libvirt,eskultety/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,olafhering/libvirt,crobinso/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,eskultety/libvirt,nertpinx/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jardasgit/libvirt,zippy2/libvirt