[stm32][i2c] use rcc_periph_reset_pulse instead of i2c_reset

i2c_reset is not implemented for I2C3 and rcc_periph_reset_pulse is the newer libopencm3 style.
@fvantienen this should fix your reset problem on navstik in absense of a fixed i2c_reset in libopencm3 (see also libopencm3/libopencm3#325)