remoteproc: Fix potential race condition in rproc_add

rproc_add adds the newly created remoteproc to a list for use by
rproc_get_by_phandle and then does some additional processing to finish
adding the remoteproc. This leaves a small window of time in which the
rproc is available in the list but not yet fully initialized, so if
another driver comes along and gets a handle to the rproc, it will be
invalid. Rearrange the code in rproc_add to make sure the rproc is added
to the list only after it has been successfuly initialized.

Fixes: 78d15ac4 ("remoteproc: introduce rproc_get_by_phandle API")
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Suman Anna <s-anna@ti.com>