LU-4472 mdc: Fix mdc_page_locate ASSERT

LU-4472 mdc: Fix mdc_page_locate ASSERT

Storing hash 0 at same as hash 1 should be okay, don't ASSERT in this
case.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I9b9488e5374d22dcfc9e7f2c969da3b02778097a
Reviewed-on: http://review.whamcloud.com/8821
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Peng Tao <bergwolf@gmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>