platform/x86: toshiba_acpi: Fix defined but not used build warnings

Fix a build warning in toshiba_acpi.c when CONFIG_PROC_FS is not enabled
by marking the unused function as __maybe_unused.

../drivers/platform/x86/toshiba_acpi.c:1685:12: warning: 'version_proc_show' defined but not used [-Wunused-function]

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Azael Avalos <coproscefalo@gmail.com>
Cc: platform-driver-x86@vger.kernel.org
Cc: Andy Shevchenko <andy@infradead.org>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>