tracing: Use __get_str() when manipulating strings

Use __get_str(str) rather than __get_dynamic_array(str) when
deadling with strings.

It is just a code cleanup, no changes on tracepoint ABI.

Link: http://lkml.kernel.org/r/[e-mail]

Cc: Trond Myklebust <[e-mail]>
Cc: Anna Schumaker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: [e-mail]
Suggested-by: Steven Rostedt <[e-mail]>
Reviewed-by: Steven Rostedt <[e-mail]>
Signed-off-by: Daniel Bristot de Oliveira <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>

fs/nfs/nfs4trace.h

···
 				len = 0;
 			__entry->error = error < 0 ? error : 0;
 			__entry->id = id;
-			memcpy(__get_dynamic_array(name), name, len);
-			((char *)__get_dynamic_array(name))[len] = 0;
+			memcpy(__get_str(name), name, len);
+			__get_str(name)[len] = 0;
 		),
 
 		TP_printk(

fs/nfs/nfstrace.h

···
 			__entry->dev = dir->i_sb->s_dev;
 			__entry->dir = NFS_FILEID(dir);
 			__entry->error = error;
-			memcpy(__get_dynamic_array(name),
+			memcpy(__get_str(name),
 				data->args.name.name, len);
-			((char *)__get_dynamic_array(name))[len] = 0;
+			__get_str(name)[len] = 0;
 		),
 
 		TP_printk(

include/trace/events/printk.h

···
 	),
 
 	TP_fast_assign(
-		memcpy(__get_dynamic_array(msg), text, len);
-		((char *)__get_dynamic_array(msg))[len] = 0;
+		memcpy(__get_str(msg), text, len);
+		__get_str(msg)[len] = 0;
 	),
 
 	TP_printk("%s", __get_str(msg))