iwlwifi: pcie: make FH debugfs file code easier to understand

The code seems fine, as buf won't be assigned when an error
is returned, but checking for the error first is easier to
understand.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

diff --cc drivers/net/wireless/iwlwifi/pcie/trans.c
Simple merge