rtc: pcf2127: fix SPI command byte for PCF2131

rtc: pcf2127: fix SPI command byte for PCF2131

PCF2131 was not responding to read/write operations using SPI. PCF2131
has a different command byte definition, compared to PCF2127/29. Added
the new command byte definition when PCF2131 is detected.

Fixes: afc505bf9039 ("rtc: pcf2127: add support for PCF2131 RTC")
Cc: stable@vger.kernel.org
Signed-off-by: Elena Popa <elena.popa@nxp.com>
Acked-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20250530104001.957977-1-elena.popa@nxp.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>