i2c: busses: i2c-designware-master: Fix misnaming of 'i2c_dw_init_master()'

Fixes the following W=1 kernel build warning(s):

 drivers/i2c/busses/i2c-designware-master.c:176: warning: expecting prototype for i2c_dw_init(). Prototype was for i2c_dw_init_master() instead

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>