checkpatch.pl: should be executable

scripts/checkpatch.pl should be executable, make it so.
Signed-off-by: NAndy Whitcroft <apw@shadowen.org>
Acked-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NJoel Schopp <jschopp@austin.ibm.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>