Style check commit hook: Ensure that formatted files need to be re-added.

Tools/astyle/check_code_style.sh

@@ -16,6 +16,9 @@ if [ -f "$FILE" ]; then
 		if [[ $PX4_ASTYLE_FIX -eq 1 ]]; then
 			${DIR}/fix_code_style.sh $FILE
 		else
+			# Make sure this file is not staged for comitting
+			git reset $FILE
+			# Provide instructions
 			echo $FILE 'bad formatting, please run "make format" or "./Tools/astyle/fix_code_style.sh' $FILE'"'
 			exit 1
 		fi