i2c: busses: xgene-slimpro: fix incorrect __init declation for probe

Fix section mismatch error during kernel build for xgene_slimpro_i2c_probe
function. It was incorrectly defined with __init declaration.

Signed-off-by: Feng Kan <fkan@apm.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>