treewide: Make remaining source files non-executable

.c and .h source files should not be executable, change
the permissions to 0644.

[ This would normally go through Andrew Morton, but his ancient
  patch-based toolchain doesn't do permission changes ]

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>