iwlwifi: dbg: decrement occurrences for all triggers

iwl_fw_dbg_collect can be called by any function that already
has the error string ready. iwl_fw_dbg_collect_trig, on the
other hand, does string formatting. The occurrences decrement
is at iwl_fw_dbg_collect_trig, instead of iwl_fw_dbg_collect,
which causes it to sometimes be skipped. Move it to the right
location.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>