rtc: tps6586x: rename so module can be autoloaded

This module is loaded by the related mfd driver which has
the needed MODULE_DEVICE_TABLE(i2c,...).

This patch fix the modalias when the rtc driver is built
as a module, so the right name is used.
Everything operates correctly when this module is builtin.

Fixes: esdc59ed3865 ("rtc: add RTC driver for TPS6586x")
Signed-off-by: Nicolas Chauvet <kwizart@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>