tee: optee: fix device enumeration error handling

Prior to this patch in optee_probe() when optee_enumerate_devices() was
called the struct optee was fully initialized. If
optee_enumerate_devices() returns an error optee_probe() is supposed to
clean up and free the struct optee completely, but will at this late
stage need to call optee_remove() instead. This isn't done and thus
freeing the struct optee prematurely.

With this patch the call to optee_enumerate_devices() is done after
optee_probe() has returned successfully and in case
optee_enumerate_devices() fails everything is cleaned up with a call to
optee_remove().

Fixes: c3fa24af

 ("tee: optee: add TEE bus device enumeration support")
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>