MAINTAINERS: Rectify entry for OPENCORES I2C BUS DRIVER

Commit 8ad69f49

 ("dt-bindings: i2c: convert ocores binding to yaml")
converts i2c-ocores.txt to opencores,i2c-ocores.yaml, but then adjust its
reference in MAINTAINERS to a slightly wrong new filename.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains about a
broken reference.

Repair this file reference in OPENCORES I2C BUS DRIVER.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>