x86/mm: Initialize pmd_idx in page_table_range_init_count()

The variable pmd_idx is not initialized for the first iteration of the
for loop.

Assign the proper value which indexes the start address.

Fixes: 719272c4

 'x86, mm: only call early_ioremap_page_table_range_init() once'
Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
Cc: tony.luck@intel.com
Cc: wangnan0@huawei.com
Cc: david.vrabel@citrix.com
Reviewed-by:  <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1436703522-29552-1-git-send-email-mhuang@redhat.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>