habanalabs: return error when failing to read/write i2c

The driver can't read/write from i2c if the device is in reset or
disabled. Therefore, return -EBUSY in those cases instead of 0.

This change also fixes a smatch warning about uninitialized variable.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>