RDMA/efa: Be consistent with success flow return value

The EFA driver is written with success oriented flows in mind, meaning
that functions should mostly end with a return 0 statement.
Error flows return their error value on their own instead of assuming
that the function will return the error at the end.

This commit fixes a bunch of functions that were not aligned with this
behavior.

Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>