fix(rmm): fix Coverity scan defects

This patch fixes Coverity scan defects below:
- In psci_rsi() function:
     Uninitialized scalar variable (UNINIT)
     uninit_use: Using uninitialized value result.
     Field result.hvc_forward.x1 is uninitialized.
  by using structure 'result' initializer, setting
  'forward_psci_call' field to 'false' and all
  other fields to 0.
- In handle_realm_rsi():
     Macro compares unsigned to 0 (NO_EFFECT)
     unsigned_compare: This greater-than-or-equal-to-zero
     comparison of an unsigned value is always true.
     ((function_id >> 0U) & 0xffffU) >= 0U.
  by removing obsolete checking code of 'function_id'
  for invalid ID value, which is handled in default
  case of 'switch(function_id)' statement.

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: I9594093f3bdb7d8276b03331192bb310ba10b94f
diff --git a/runtime/rsi/psci.c b/runtime/rsi/psci.c
index 7ab7fd6..4a62685 100644
--- a/runtime/rsi/psci.c
+++ b/runtime/rsi/psci.c
@@ -245,7 +245,7 @@
 			    unsigned long arg1,
 			    unsigned long arg2)
 {
-	struct psci_result result;
+	struct psci_result result = { false };
 
 	switch (function_id) {
 	case SMC32_PSCI_VERSION:
@@ -262,7 +262,7 @@
 		arg0 = (unsigned int)arg0;
 		arg1 = (unsigned int)arg1;
 		arg2 = (unsigned int)arg2;
-		/* Fall through */
+		FALLTHROUGH;
 	case SMC64_PSCI_CPU_ON:
 		result = psci_cpu_on(rec, arg0, arg1, arg2);
 		break;