x86/mm: add testmmiotrace MODULE_DESCRIPTION()

Fix the following 'make W=1' warning:

WARNING: modpost: missing MODULE_DESCRIPTION() in arch/x86/mm/testmmiotrace.o

Link: https://lkml.kernel.org/r/20240730-module_description_orphans-v1-2-7094088076c8@quicinc.com
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Alistar Popple <alistair@popple.id.au>
Cc: Andrew Jeffery <andrew@codeconstruct.com.au>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eddie James <eajames@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jeremy Kerr <jk@ozlabs.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Karol Herbst <karolherbst@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nouveau <nouveau@lists.freedesktop.org>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/x86/mm/testmmiotrace.c

@@ -144,3 +144,4 @@ static void __exit cleanup(void)
 module_init(init);
 module_exit(cleanup);
 MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Test module for mmiotrace");