docs: timekeeping: Use correct prototype for deprecated functions

Use the correct prototypes for do_gettimeofday(), getnstimeofday() and
getnstimeofday64(). All of these returned void and passed the return
value by reference. This should make the documentation of their
deprecation and replacements easier to search for.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200414221222.23996-1-chris.packham@alliedtelesis.co.nzSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/timekeeping.rst

@@ -154,9 +154,9 @@ architectures. These are the recommended replacements:
 
 	Use ktime_get() or ktime_get_ts64() instead.
 
-.. c:function:: struct timeval do_gettimeofday( void )
-		struct timespec getnstimeofday( void )
-		struct timespec64 getnstimeofday64( void )
+.. c:function:: void do_gettimeofday( struct timeval * )
+		void getnstimeofday( struct timespec * )
+		void getnstimeofday64( struct timespec64 * )
 		void ktime_get_real_ts( struct timespec * )
 
 	ktime_get_real_ts64() is a direct replacement, but consider using