i2c: pci1xxxx: prevent signed integer overflow

Some constants need 'UL' markings, otherwise they are shifted into the
sign bit.

Fixes: 36169369 ("i2c: microchip: pci1xxxx: Add driver for I2C host controller in multifunction endpoint of pci1xxxx switch")
Signed-off-by: Wolfram Sang <wsa@kernel.org>