cpufreq: ondemand:Fix NULL check for dbs_info->cur_policy

dbs_info->cur_policy can go NULL when processing
CPUFREQ_GOV_LIMITS, NULL check is required
before processing it

Change-Id: Iba99b563e230835dfcd24573335065d68ad25821
CRs-fixed: 576272
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>