Fix test-i2c leak, and mctp_pktbuf storage alignment

- Ensure mctp_pktbuf storage is correctly aligned
- Deallocate mctp and i2c instances to avoid failure with asan.

These previously succeeded in CI so are both fixed in this commit.

Fixes: e5b941d9d764 ("i2c: Add binding for MCTP over I2C transport")
Fixes: 4a09e1dc4883 ("core: Reuse buffers for tx, allow message pools")
Change-Id: I747bfff6faf3a5b0a982ae266bcef02ecbc4ee8a
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
diff --git a/tests/test_bridge.c b/tests/test_bridge.c
index 73705ba..40d5fb6 100644
--- a/tests/test_bridge.c
+++ b/tests/test_bridge.c
@@ -19,7 +19,7 @@
 	int rx_count;
 	int tx_count;
 	uint8_t last_pkt_data;
-	uint8_t tx_storage[MCTP_PKTBUF_SIZE(MCTP_BTU)];
+	uint8_t tx_storage[MCTP_PKTBUF_SIZE(MCTP_BTU)] PKTBUF_STORAGE_ALIGN;
 };
 
 struct test_ctx {