Kernel: Use Userspace<T> for the gethostname syscall

Author: https://github.com/bgianfo
Commit: 1d9554f470
Pull-request: https://github.com/SerenityOS/serenity/pull/3062
Reviewed-by: https://github.com/awesomekling

Kernel/Syscalls/hostname.cpp

@@ -31,7 +31,7 @@ namespace Kernel {
 extern String* g_hostname;
 extern Lock* g_hostname_lock;
 
-int Process::sys$gethostname(char* buffer, ssize_t size)
+int Process::sys$gethostname(Userspace<char*> buffer, ssize_t size)
 {
     REQUIRE_PROMISE(stdio);
     if (size < 0)