repart: return 1 from probe_sector_size_prefer_ioctl() on block device success

repart: return 1 from probe_sector_size_prefer_ioctl() on block device success

probe_sector_size() returns 1 when it successfully determines the sector size,
0 when falling back to the default. blockdev_get_sector_size() returns 0 on
success. probe_sector_size_prefer_ioctl() was passing blockdev_get_sector_size()
return value through directly, so caller is checking r > 0 to detect a
successfully probed sector size never saw it for block devices.

In context_load_partition_table(), this caused fs_secsz to stay at 4096 bytes
even on 512-byte sector block devices, making verity hash partition sizes wrong
unless --sector-size=512 was passed explicitly.

Fix by returning 1 on success from the block device path to match probe_sector_size()
convention.