MAINTAINERS: add the Polarfire SoC's i2c driver

Add the newly added i2c controller driver to the existing entry for
PolarFire SoC.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Link: https://lore.kernel.org/r/20220810140243.2685416-3-conor.dooley@microchip.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>