fix: explicit boolean for `share_state` pointer

Use explicit booleans when checking the validity of a reference
to a `share_state` strucuture.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I6a1f0695480afe319fbf40085b699fe9fb41bf35
diff --git a/src/ffa_memory.c b/src/ffa_memory.c
index 22aba6f..bd8f197 100644
--- a/src/ffa_memory.c
+++ b/src/ffa_memory.c
@@ -1594,7 +1594,7 @@
 	 * matches.
 	 */
 	share_state = get_share_state(share_states, handle);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose(
 			"Invalid handle %#x for memory send continuation.\n",
 			handle);
@@ -1720,7 +1720,7 @@
 	share_state = allocate_share_state(share_states, share_func,
 					   memory_region, fragment_length,
 					   FFA_MEMORY_HANDLE_INVALID);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose("Failed to allocate share state.\n");
 		mpool_free(page_pool, memory_region);
 		ret = ffa_error(FFA_NO_MEMORY);
@@ -2470,7 +2470,7 @@
 
 	share_states = share_states_lock();
 	share_state = get_share_state(share_states, handle);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose("Invalid handle %#x for FFA_MEM_RETRIEVE_REQ.\n",
 			     handle);
 		ret = ffa_error(FFA_INVALID_PARAMETERS);
@@ -2724,7 +2724,7 @@
 
 	share_states = share_states_lock();
 	share_state = get_share_state(share_states, handle);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose("Invalid handle %#x for FFA_MEM_FRAG_RX.\n",
 			     handle);
 		ret = ffa_error(FFA_INVALID_PARAMETERS);
@@ -2905,7 +2905,7 @@
 
 	share_states = share_states_lock();
 	share_state = get_share_state(share_states, handle);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose("Invalid handle %#x for FFA_MEM_RELINQUISH.\n",
 			     handle);
 		ret = ffa_error(FFA_INVALID_PARAMETERS);
@@ -3031,7 +3031,7 @@
 	share_states = share_states_lock();
 
 	share_state = get_share_state(share_states, handle);
-	if (!share_state) {
+	if (share_state == NULL) {
 		dlog_verbose("Invalid handle %#x for FFA_MEM_RECLAIM.\n",
 			     handle);
 		ret = ffa_error(FFA_INVALID_PARAMETERS);