rtc: ds1307: Detect oscillator fail on mcp794xx

This patch enables the detection of the oscillator failure on mcp794xx chips.

Co-developed-by: Szentendrei, Tamás <szentendrei.tamas@prolan.hu>
Signed-off-by: Szentendrei, Tamás <szentendrei.tamas@prolan.hu>
Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Link: https://lore.kernel.org/r/20240611072411.671600-1-csokas.bence@prolan.hu


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