tracing/filters: strloc should be unsigned short

I forgot to update filter code accordingly in
"tracing/events: change the type of __str_loc_item to unsigned short"
(commt b0aae68c)

It can cause system crash:

 # echo 1 > tracing/events/irq/irq_handler_entry/enable
 # echo 'name == eth0' > tracing/events/irq/irq_handler_entry/filter

[ Impact: fix crash while filtering on __string() field ]

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A35B905.3090500@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>