staging: comedi: comedi_compat32.h: checkpatch.pl --strict cleanup

Fix the checkpatch.pl --strict issues:

CHECK: extern prototypes should be avoided in .h files
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_compat32.h

@@ -25,8 +25,7 @@
 #ifdef CONFIG_COMPAT
 
 struct file;
-extern long comedi_compat_ioctl(struct file *file, unsigned int cmd,
-				unsigned long arg);
+long comedi_compat_ioctl(struct file *, unsigned int cmd, unsigned long arg);
 
 #else /* CONFIG_COMPAT */