i2c: isch: Unify the name of the variable to hold an error code

There are two different names used for the variable that holds
an error code. Unify to use one variant in all cases.

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