spi/omap: Correct the error path

Currently McSPI driver doesnt follow correct failure fallback steps
attempting to correct the same.

Also:
- label names changed to give meaningful names.
- Setting the driver data to NULL in remove

Signed-off-by: Hebbar, Gururaja <gururaja.hebbar@ti.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>