Fix compiler warning

diff --git a/INA3221.h b/INA3221.h
index bf09c8e..3fc7ad7 100644
--- a/INA3221.h
+++ b/INA3221.h
@@ -109,7 +109,7 @@ class INA3221 {
         uint16_t ch2_en : 1;
         uint16_t ch1_en : 1;
         uint16_t reset : 1;
-    } __attribute__((packed)) conf_reg_t;
+    } __attribute__((packed, aligned(sizeof(uint16_t)))) conf_reg_t;
 
     // Mask/Enable register
     typedef struct {
@@ -129,7 +129,7 @@ class INA3221 {
         uint16_t shunt_sum_en_ch2 : 1;
         uint16_t shunt_sum_en_ch1 : 1;
         uint16_t reserved : 1;
-    } __attribute__((packed)) masken_reg_t;
+    } __attribute__((packed, aligned(sizeof(uint16_t)))) masken_reg_t;
 
     // Arduino's I2C library
     TwoWire *_i2c;