Gekko: Make UReg_FPSCR's single argument constructor explicit

Prevent implicit conversions to UReg_FPSCR. Given the semantics of a
random magic value and the FPSCR are different, make explicit
conversions a requirement to signify intent.

Source/Core/Core/PowerPC/Gekko.h

@@ -475,7 +475,7 @@ union UReg_FPSCR
   u32 Hex = 0;
 
   UReg_FPSCR() = default;
-  UReg_FPSCR(u32 hex_) : Hex{hex_} {}
+  explicit UReg_FPSCR(u32 hex_) : Hex{hex_} {}
 };
 
 // Hardware Implementation-Dependent Register 0

Source/Core/Core/PowerPC/PowerPC.cpp

@@ -128,7 +128,7 @@ static void ResetRegisters()
   ppcState.spr[SPR_ECID_M] = 0x1840c00d;
   ppcState.spr[SPR_ECID_L] = 0x82bb08e8;
 
-  ppcState.fpscr = 0;
+  ppcState.fpscr.Hex = 0;
   ppcState.pc = 0;
   ppcState.npc = 0;
   ppcState.Exceptions = 0;