shdma: fix initialization error handling

1/ Error handling code following a kzalloc should free the allocated data.
2/ Report an error when no platform data is detected

Both problems fixed by moving the platform data check before the allocation,
and allows a goto to be killed.

Reported-by: Julia Lawall <julia@diku.dk>
Acked-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>