drivers: modem: initialized variables

This PR is related to the following Zephyr PR:
#81431
Some compilers (e.g. arm-zephyr-eabi-gcc) don't understand
the K_SPINLOCK() macro and therefore do warn about
uninitialized variables in the modem related modules.

Signed-off-by: Fabian Kainka <[email protected]>

Author: FKainka

subsys/modem/modem_cmux.c

@@ -1108,7 +1108,7 @@ static int modem_cmux_dlci_pipe_api_transmit(void *data, const uint8_t *buf, siz
 {
 	struct modem_cmux_dlci *dlci = (struct modem_cmux_dlci *)data;
 	struct modem_cmux *cmux = dlci->cmux;
-	int ret;
+	int ret = 0;
 
 	K_SPINLOCK(&cmux->work_lock) {
 		if (!cmux->attached) {
@@ -1345,7 +1345,7 @@ int modem_cmux_connect(struct modem_cmux *cmux)
 
 int modem_cmux_connect_async(struct modem_cmux *cmux)
 {
-	int ret;
+	int ret = 0;
 
 	if (k_event_test(&cmux->event, MODEM_CMUX_EVENT_CONNECTED_BIT)) {
 		return -EALREADY;

subsys/modem/modem_pipelink.c

@@ -27,7 +27,7 @@ void modem_pipelink_attach(struct modem_pipelink *link,
 
 bool modem_pipelink_is_connected(struct modem_pipelink *link)
 {
-	bool connected;
+	bool connected = false;
 
 	K_SPINLOCK(&link->spinlock) {
 		connected = link->connected;