[window-covering] Fix compilation error on some compilers (#16491)

OperationalStatus structure contains enum class bitfields,
which on some compilers (e.g. GCC prior to 9.3) generates
"is too small to hold all values of
‘enum class OperationalState’" warning. It is a default
warning that cannot be suppressed.

Since OperationalStatus it not stored directly in the
attribute table, but it is rather used to exchange decoded
components of the attribute with the application, the
bitfield usage is not really valuable. Switch to normal
structure members for greater portability.

src/app/clusters/window-covering-server/window-covering-server.h

@@ -67,13 +67,13 @@ enum class OperationalState : uint8_t
 };
 static_assert(sizeof(OperationalState) == sizeof(uint8_t), "OperationalState Size is not correct");
 
+// Decoded components of the OperationalStatus attribute
 struct OperationalStatus
 {
-    OperationalState global : 2; // bit 0-1 M
-    OperationalState lift : 2;   // bit 2-3 LF
-    OperationalState tilt : 2;   // bit 4-5 TL
+    OperationalState global; // bit 0-1 M
+    OperationalState lift;   // bit 2-3 LF
+    OperationalState tilt;   // bit 4-5 TL
 };
-static_assert(sizeof(OperationalStatus) == sizeof(uint8_t), "OperationalStatus Size is not correct");
 
 struct SafetyStatus
 {