iio: event_monitor: add linear acceleration modifiers

Following the introduction of IIO linear acceleration modifiers, update the
event_monitor tool accordingly.

Signed-off-by: Andrea Merello <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

tools/iio/iio_event_monitor.c

···
 	[IIO_MOD_PM4] = "pm4",
 	[IIO_MOD_PM10] = "pm10",
 	[IIO_MOD_O2] = "o2",
+	[IIO_MOD_LINEAR_X] = "linear_x",
+	[IIO_MOD_LINEAR_Y] = "linear_y",
+	[IIO_MOD_LINEAR_Z] = "linear_z",
 };
 
 static bool event_is_known(struct iio_event_data *event)