drivers: Add 'U' to unsigned variable assignments

Add 'U' to a value when assigning it to an unsigned variable.
MISRA-C rule 7.2

Signed-off-by: Patrik Flykt <patrik.flykt@intel.com>
diff --git a/drivers/interrupt_controller/shared_irq.c b/drivers/interrupt_controller/shared_irq.c
index f18ba38..50242a6 100644
--- a/drivers/interrupt_controller/shared_irq.c
+++ b/drivers/interrupt_controller/shared_irq.c
@@ -29,7 +29,7 @@
 	const struct shared_irq_config *config = dev->config->config_info;
 	u32_t i;
 
-	for (i = 0; i < config->client_count; i++) {
+	for (i = 0U; i < config->client_count; i++) {
 		if (!clients->client[i].isr_dev) {
 			clients->client[i].isr_dev = isr_dev;
 			clients->client[i].isr_func = isr_func;
@@ -50,7 +50,7 @@
 	const struct shared_irq_config *config = dev->config->config_info;
 	u32_t i;
 
-	for (i = 0; i < config->client_count; i++) {
+	for (i = 0U; i < config->client_count; i++) {
 		if (clients->client[i].isr_dev == isr_dev) {
 			clients->client[i].enabled = 1;
 			irq_enable(config->irq_num);
@@ -64,7 +64,7 @@
 {
 	u32_t i;
 
-	for (i = 0; i < count; i++) {
+	for (i = 0U; i < count; i++) {
 		if (clients->client[i].enabled) {
 			return 0;
 		}
@@ -82,7 +82,7 @@
 	const struct shared_irq_config *config = dev->config->config_info;
 	u32_t i;
 
-	for (i = 0; i < config->client_count; i++) {
+	for (i = 0U; i < config->client_count; i++) {
 		if (clients->client[i].isr_dev == isr_dev) {
 			clients->client[i].enabled = 0;
 			if (last_enabled_isr(clients, config->client_count)) {
@@ -100,7 +100,7 @@
 	const struct shared_irq_config *config = dev->config->config_info;
 	u32_t i;
 
-	for (i = 0; i < config->client_count; i++) {
+	for (i = 0U; i < config->client_count; i++) {
 		if (clients->client[i].isr_dev) {
 			clients->client[i].isr_func(clients->client[i].isr_dev);
 		}