memory: fsl_ifc: fix leak of IO mapping on probe failure

On probe error the driver should unmap the IO memory.  Smatch reports:

  drivers/memory/fsl_ifc.c:298 fsl_ifc_ctrl_probe() warn: 'fsl_ifc_ctrl_dev->gregs' not released on lines: 298.

Fixes: a20cbdef ("powerpc/fsl: Add support for Integrated Flash Controller")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210527154322.81253-1-krzysztof.kozlowski@canonical.com