MAINTAINERS: adjust XLP9XX I2C DRIVER after removing the devicetree binding

Commit 0e5f8977 ("dt-bindings: Remove Netlogic bindings") removes the
devicetree binding i2c-xlp9xx.txt, but misses to adjust the reference in
MAINTAINERS.

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

Remove the file reference to i2c-xlp9xx.txt in XLP9XX I2C DRIVER.

As commit ef99066c ("i2c: Remove Netlogic XLP variant") explains, the
i2c-xlp9xx driver is still used by the Cavium ThunderX2 platform. So, keep
the XLP9XX I2C DRIVER section in MAINTAINERS with its reference to
drivers/i2c/busses/i2c-xlp9xx.c.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>