pstore: Correct the max_dump_cnt clearing of ramoops

In case that ramoops_init_przs failed, max_dump_cnt won't be reset to
zero in error handle path.

Signed-off-by: Liu ShuoX <shuox.liu@intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>