rtc: sysfs: make name uniform

The name sysfs attribute is not useful in its current form because of all
the drivers:
 - 3 are using the feature correctly
 - 2 are clearly misusing it
 - 60 are using driver.name, either directly or indirectly
 - 46 are using pdev->name
 - 8 are using client->name
 - 31 are using a variation of driver.name (addition or removal of rtc-,
   -rtc, _rtc, rtc_)

Make it uniform and use the driver name and the device name.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>