hugetlb: fix/remove uninitialized variable in remove_inode_hugepages

hugetlb: fix/remove uninitialized variable in remove_inode_hugepages

Code introduced for the routine remove_inode_hugepages by patch "hugetlb:
handle truncate racing with page faults", incorrectly uses a variable
m_index.  This is a remnant from a previous version of the code when under
development.  Use the correct variable 'index' and remove 'm_index' from
the routine.

Link: https://lkml.kernel.org/r/Ywepr7C2X20ZvLdn@monkey
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>