firmware: stratix10-svc: Fix an NULL vs IS_ERR() bug in probe

[ Upstream commit e1d6ca04 ]

The svc_create_memory_pool() function returns error pointers.  It never
returns NULL.  Fix the check.

Fixes: 7ca5ce89

 ("firmware: add Intel Stratix10 service layer driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/5f9a8cb4-5a4f-460b-9cdc-2fae6c5b7922@kili.mountain
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>