qcacld-3.0: Validate user input for null termination

In hdd_dns_make_name_query() the parameter string is a user controlled
input. The driver assumes that the input is null terminated string and
accordingly the exit condition of the loop is specified. In case the
user sends input with no null termination then it can lead to possible
OOB scenario.

Add a null termination validation on the string so that any erroneous
input is filtered.

Change-Id: I2abb4875569c508179c4488347f7c9aae0666332
CRs-Fixed: 2342812