rtc/mc13783: protect rtc {,un}registration by mc13783 lock

rtc/mc13783: protect rtc {,un}registration by mc13783 lock

This is to protect from interrupt handlers using an unregistered rtc
device.

To assert that the reset irq is considered now before the rtc is
registered the corresponding status is checked before.

Signed-off-by: Uwe Kleine-König <[email protected]>
Cc: Alessandro Zummo <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Valentin Longchamp <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Samuel Ortiz <[email protected]>
Cc: Dmitry Torokhov <[email protected]>
Cc: Luotao Fu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>