checkpatch.pl: should be executable

scripts/checkpatch.pl should be executable, make it so.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Joel Schopp <jschopp@austin.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>