arm: mvebu: fix vendor prefix typo in kirkwood-synology.dtsi

arm: mvebu: fix vendor prefix typo in kirkwood-synology.dtsi

As reported by Andrew, the vendor prefix for Seiko Instruments, Inc.
S-35390A I2C RTC chip in kirkwood-synology.dtsi has a typo (ssi
instead of sii). This patches fixes it.

Note: i2c devices ignore the optional vendor prefix, which explains
why it worked with the typo and also why there is no backward
compatibility issues with the fix.

Reported-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Link: https://lkml.kernel.org/r/0444140a267d982c3e5f5f2b7b5f2dc41d010e2a.1416613429.git.arno@natisbad.org
Signed-off-by: Jason Cooper <jason@lakedaemon.net>