sata_dwc_460ex: fix resource leak on error path

DMA mapped IO should be unmapped on the error path in probe() and
unconditionally on remove().

Fixes: 62936009 ([libata] Add 460EX on-chip SATA driver, sata_dwc_460ex)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>