i2c: axxia: enable clock before calling clk_get_rate()

axxia_i2c_init() uses clk_get_rate() for idev->i2c_clk. clk_get_rate()
should only be called if the clock is enabled, so ensure that by moving
the clk_prepare_enable() call before the call to axxia_i2c_init().

Found by Linux Driver Verification project (linuxtesting.org).

Fixes: 08678b85 ("i2c: axxia: Add I2C driver for AXM55xx")
Signed-off-by: Tobias Jordan <Tobias.Jordan@elektrobit.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>