Pull i2c fixes from Wolfram Sang:
 "Some I2C core improvements to prevent NULL pointer usage and a
  MAINTAINERS update"

* 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux:
  i2c: slave: add sanity check when unregistering
  i2c: slave: improve sanity check when registering
  MAINTAINERS: Update GENI I2C maintainers list
  i2c: also convert placeholder function to return errno