Input: synaptics - hide unused smbus_pnp_ids[] array

Input: synaptics - hide unused smbus_pnp_ids[] array

When SMBUS is disabled, this is never referenced, causing a W=1 warning:

drivers/input/mouse/synaptics.c:164:27: error: 'smbus_pnp_ids' defined but not used [-Werror=unused-const-variable=]

Hide the array behind the same #ifdef as the code referencing it.

Fixes: e839ffab0289 ("Input: synaptics - add support for Intertouch devices")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250225145451.1141995-1-arnd@kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>