constexpr -> const

We don't need constexpr and this was restricting compiler to c++11 or
later

MS5837.cpp

@@ -8,6 +8,13 @@
 #define MS5837_CONVERT_D1_8192    0x4A
 #define MS5837_CONVERT_D2_8192    0x5A
 
+const float MS5837::Pa = 100.0f;
+const float MS5837::bar = 0.001f;
+const float MS5837::mbar = 1.0f;
+
+const uint8_t MS5837::MS5837_30BA = 0;
+const uint8_t MS5837::MS5837_02BA = 1;
+
 MS5837::MS5837() {
 	fluidDensity = 1029;
 }

MS5837.h

@@ -41,12 +41,12 @@ THE SOFTWARE.
 
 class MS5837 {
 public:
-	static constexpr float Pa = 100.0f;
-	static constexpr float bar = 0.001f;
-	static constexpr float mbar = 1.0f;
+	static const float Pa;
+	static const float bar;
+	static const float mbar;
 
-	static constexpr uint8_t MS5837_30BA = 0;
-	static constexpr uint8_t MS5837_02BA = 1;
+	static const uint8_t MS5837_30BA;
+	static const uint8_t MS5837_02BA;
 
 	MS5837();