i2c: isch: Utilize temporary variable to hold device pointer

Introduce a temporary variable to hold a device pointer.
It can be utilized in the ->probe() and save a bit of LoCs.
To make it consistent, rename currently used dev to pdev.

While at it, convert the only error message to dev_err_probe().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>