i2c: core: Add stub for i2c_verify_client() if !CONFIG_I2C

i2c: core: Add stub for i2c_verify_client() if !CONFIG_I2C

If I2C is not compiled, there is no way we should see a call to
i2c_verify_client() on a device that is an i2c client. As such,
provide a stub to return NULL to resolve an associated build failure.

The build is failing with this link error
ld: fxls8962af-core.o: in function `fxls8962af_fifo_transfer':
fxls8962af-core.c: undefined reference to `i2c_verify_client'

Reported-by: Tom Rix <trix@redhat.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Fixes: af959b7b96b8 ("iio: accel: fxls8962af: fix errata bug E3 - I2C burst reads")
Reviewed-by: Sean Nyekjaer <sean@geanix.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Link: https://lore.kernel.org/r/20210603165835.3594557-1-jic23@kernel.org