rtc: mark if rtc-cmos drivers were successfully registered

rtc-cmos has two drivers, one PNP and one platform.  When PNP has not
succeeded probing, platform is registered.  However, it tries to
unregister both drivers unconditionally, instead of only unregistering
those that were successfully registered.  This causes runtime warnings to
be emitted from the driver core code.

Fix this with a boolean variable for each driver indicating whether
registering was successful.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Alessandro Zummo <alessandro.zummo@towertech.it>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Brownell <david-b@pacbell.net>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Greg KH <greg@kroah.com>
Cc: Ozan Caglayan <ozan@pardus.org.tr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>