tools/checkpatch.sh: remove flag --no-tree

Commit c5d8988316 ("checkpatch.pl:
check for openocd tree, not for kernel tree") has already fixed
the check for OpenOCD tree, thus we do not need to skip it in the
shell wrapper.

Remove flag --no-tree from the shell wrapper.

Change-Id: I8be497258624d89bde7742fee141a8f56bf9188e
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5110
Tested-by: jenkins

tools/checkpatch.sh

@@ -2,4 +2,4 @@
 #
 
 since=${1:-HEAD^}
-git format-patch -M --stdout $since | tools/scripts/checkpatch.pl - --no-tree
+git format-patch -M --stdout $since | tools/scripts/checkpatch.pl -