lib: arm_ffa: Continue FFA init if MEM_RETRIEVE_REQ is not supported

KVM does not support calling MEM_RETRIEVE_REQ from
a pVM so this commit allows the FFA init hook to
continue if Trusty is running in non-secure.

Bug: None
Change-Id: I5d7c5dbb0631b95001a06f8a562011e5a59a7f5d

lib/arm_ffa/arm_ffa.c

diff --git a/lib/arm_ffa/arm_ffa.c b/lib/arm_ffa/arm_ffa.c
index 9656664..6fbe3c7 100644
--- a/lib/arm_ffa/arm_ffa.c
+++ b/lib/arm_ffa/arm_ffa.c
@@ -1052,10 +1052,7 @@
     }
     if (!is_implemented) {
         TRACEF("FFA_MEM_RETRIEVE_REQ is not implemented\n");
-        return ERR_NOT_SUPPORTED;
-    }
-
-    if (ref_count_num_bits < 64) {
+    } else if (ref_count_num_bits < 64) {
         /*
          * Expect 64 bit reference count. If we don't have it, future calls to
          * SMC_FC_FFA_MEM_RETRIEVE_REQ can fail if we receive the same handle