i2c: mlxbf: select CONFIG_I2C_SLAVE

If this is not enabled, the interfaces used in this driver do not work:

drivers/i2c/busses/i2c-mlxbf.c:1888:3: error: implicit declaration of function 'i2c_slave_event' [-Werror,-Wimplicit-function-declaration]
i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
^
drivers/i2c/busses/i2c-mlxbf.c:1888:26: error: use of undeclared identifier 'I2C_SLAVE_WRITE_REQUESTED'
i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
^
drivers/i2c/busses/i2c-mlxbf.c:1890:32: error: use of undeclared identifier 'I2C_SLAVE_WRITE_RECEIVED'
ret = i2c_slave_event(slave, I2C_SLAVE_WRITE_RECEIVED,
^
drivers/i2c/busses/i2c-mlxbf.c:1892:26: error: use of undeclared identifier 'I2C_SLAVE_STOP'
i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
^

Fixes: b5b5b32081cd ("i2c: mlxbf: I2C SMBus driver for Mellanox BlueField SoC")
Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Khalil Blaiech <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/Kconfig

···
 config I2C_MLXBF
         tristate "Mellanox BlueField I2C controller"
         depends on MELLANOX_PLATFORM && ARM64
+	select I2C_SLAVE
         help
           Enabling this option will add I2C SMBus support for Mellanox BlueField
           system.