mtd: spear_smi: Remove default partition information from driver

Additionally, after failing in mtd_device_parse_register(), the driver
unmap/free code is now executed.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>