LU-9814 ldiskfs: restore simple_strtol in prealloc

LU-9814 ldiskfs: restore simple_strtol in prealloc

Since kstrtol needs a null-terminor string so we
back to use simple_strtol in prealloc patches.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: I331308d830fbeef9c00156bb8c14b43651d66420
Reviewed-on: https://review.whamcloud.com/28553
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>