ppdev: add header include guard

Add a header include guard just in case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://lore.kernel.org/r/20190728152739.9249-1-yamada.masahiro@socionext.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/linux/ppdev.h

@@ -15,6 +15,9 @@
  * Added PPGETMODES/PPGETMODE/PPGETPHASE, Fred Barnes <frmb2@ukc.ac.uk>, 03/01/2001
  */
 
+#ifndef _UAPI_LINUX_PPDEV_H
+#define _UAPI_LINUX_PPDEV_H
+
 #define PP_IOCTL	'p'
 
 /* Set mode for read/write (e.g. IEEE1284_MODE_EPP) */
@@ -97,4 +100,4 @@ struct ppdev_frob_struct {
 /* only masks user-visible flags */
 #define PP_FLAGMASK	(PP_FASTWRITE | PP_FASTREAD | PP_W91284PIC)
 
-
+#endif /* _UAPI_LINUX_PPDEV_H */