iio: inv_mpu6050: Fix use-after-free in ACPI code

In some cases this can result in incorrectly returning a negative value
from asus_acpi_get_sensor_info and the AK8963 magnetometer failing to
show up.

Note cpm is an alias for buffer.pointer which isn't apparent in this
patch on it's own.

Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Crestez Dan Leonard <leonard.crestez@intel.com>
Acked-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/imu/inv_mpu6050/inv_mpu_acpi.c

@@ -56,6 +56,7 @@ static int asus_acpi_get_sensor_info(struct acpi_device *adev,
 	int i;
 	acpi_status status;
 	union acpi_object *cpm;
+	int ret;
 
 	status = acpi_evaluate_object(adev->handle, "CNF0", NULL, &buffer);
 	if (ACPI_FAILURE(status))
@@ -82,10 +83,10 @@ static int asus_acpi_get_sensor_info(struct acpi_device *adev,
 			}
 		}
 	}
-
+	ret = cpm->package.count;
 	kfree(buffer.pointer);
 
-	return cpm->package.count;
+	return ret;
 }
 
 static int acpi_i2c_check_resource(struct acpi_resource *ares, void *data)