pmic:i2c: Replace legacy I2C_SET_BUS macro with i2c_set_bus_num()

After introduction of unified i2c model, the I2C_SET_BUS() macro is regarded
as obsolete.
Hence it is replaced with i2c_set_bus_num() function call.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Tom Rini <trini@ti.com>