modpost: use proper kernel style for autogenerated files

If the kernel build process is creating files automatically, the least
it can do is create them in a properly formatted manner.  Sure, it's a
minor issue, but being consistent is nice.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>