Initialize data->config_lock mutex before it is used by the driver code.

This fixes following warning on Odroid XU3 boards:

INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 5 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc7-next-20180115-00001-gb75575dee3f2 #107
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c0111504>] (unwind_backtrace) from [<c010dbec>] (show_stack+0x10/0x14)
[<c010dbec>] (show_stack) from [<c09b3f74>] (dump_stack+0x90/0xc8)
[<c09b3f74>] (dump_stack) from [<c0179528>] (register_lock_class+0x1c0/0x59c)
[<c0179528>] (register_lock_class) from [<c017bd1c>] (__lock_acquire+0x78/0x1850)
[<c017bd1c>] (__lock_acquire) from [<c017de30>] (lock_acquire+0xc8/0x2b8)
[<c017de30>] (lock_acquire) from [<c09ca59c>] (__mutex_lock+0x60/0xa0c)
[<c09ca59c>] (__mutex_lock) from [<c09cafd0>] (mutex_lock_nested+0x1c/0x24)
[<c09cafd0>] (mutex_lock_nested) from [<c068b0d0>] (ina2xx_set_shunt+0x70/0xb0)
[<c068b0d0>] (ina2xx_set_shunt) from [<c068b218>] (ina2xx_probe+0x88/0x1b0)
[<c068b218>] (ina2xx_probe) from [<c0673d90>] (i2c_device_probe+0x1e0/0x2d0)
[<c0673d90>] (i2c_device_probe) from [<c053a268>] (driver_probe_device+0x2b8/0x4a0)
[<c053a268>] (driver_probe_device) from [<c053a54c>] (__driver_attach+0xfc/0x120)
[<c053a54c>] (__driver_attach) from [<c05384cc>] (bus_for_each_dev+0x58/0x7c)
[<c05384cc>] (bus_for_each_dev) from [<c0539590>] (bus_add_driver+0x174/0x250)
[<c0539590>] (bus_add_driver) from [<c053b5e0>] (driver_register+0x78/0xf4)
[<c053b5e0>] (driver_register) from [<c0675ef0>] (i2c_register_driver+0x38/0xa8)
[<c0675ef0>] (i2c_register_driver) from [<c0102b40>] (do_one_initcall+0x48/0x18c)
[<c0102b40>] (do_one_initcall) from [<c0e00df0>] (kernel_init_freeable+0x110/0x1d4)
[<c0e00df0>] (kernel_init_freeable) from [<c09c8120>] (kernel_init+0x8/0x114)
[<c09c8120>] (kernel_init) from [<c01010b4>] (ret_from_fork+0x14/0x20)

Fixes: 5d389b12 ("hwmon: (ina2xx) Make calibration register value fixed")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>