storage: Resolve Coverity OVERFLOW_BEFORE_WIDEN

Coverity complains that when multiplying to 32 bit values that eventually
will be stored in a 64 bit value that it's possible the math could
overflow unless one of the values being multiplied is type cast to
the proper size.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

src/storage/storage_backend_disk.c

@@ -560,7 +560,7 @@ virStorageBackendDiskPartBoundaries(virStoragePoolObjPtr pool,
     unsigned long long extraBytes = 0;
     unsigned long long alignedAllocation = allocation;
     virStoragePoolSourceDevicePtr dev = &pool->def->source.devices[0];
-    unsigned long long cylinderSize = dev->geometry.heads *
+    unsigned long long cylinderSize = (unsigned long long)dev->geometry.heads *
                                       dev->geometry.sectors * SECTOR_SIZE;
 
     VIR_DEBUG("find free area: allocation %llu, cyl size %llu", allocation,