zephyr: Replace zephyr integer types with C99 types.

Zephyr v2.4.0 stopped using custom integer types in favor of C99 types
instead.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>

ports/zephyr/machine_i2c.c

@@ -97,7 +97,7 @@ STATIC int machine_hard_i2c_transfer_single(mp_obj_base_t *self_in, uint16_t add
     struct i2c_msg msg;
     int ret;
 
-    msg.buf = (u8_t *)buf;
+    msg.buf = (uint8_t *)buf;
     msg.len = len;
     msg.flags = 0;
 

ports/zephyr/zephyr_storage.c

@@ -146,7 +146,7 @@ typedef struct _zephyr_flash_area_obj_t {
     const struct flash_area *area;
     int block_size;
     int block_count;
-    u8_t id;
+    uint8_t id;
 } zephyr_flash_area_obj_t;
 
 STATIC void zephyr_flash_area_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {