rq_stats: Compilation error fix for 32bit kernel

This fixes below compilation error for 32bit kernel
build. Comparison of distinct pointer types long long
and unsigned long long. Change is to use uint64_t to
fix this.

Change-Id: I4a097a1fe8f6d4816c6049f2220934182d1381ef
Signed-off-by: Lijuan Gao <lijuang@codeaurora.org>