rtc: bq32k: remove redundant check

removing below static analysis error:
(error) Possible null pointer dereference: client

if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
							^^^^^^^
Error comes because client is dereferenced before NULL check.
So probably NULL this check is not required.

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>