i2c: piix4: Fix a memory leak in the EFCH MMIO support

In the Linux kernel, the following vulnerability has been resolved: i2c: piix4: Fix a memory leak in the EFCH MMIO support The recently added support for EFCH MMIO regions introduced a memory leak in that code path. The leak is caused by the fact that release_resource() merely removes the resource from the tree but does not free its memory. We need to call release_mem_region() instead, which does free the memory. As a nice side effect, this brings back some symmetry between the legacy and MMIO paths.