fix #355 possible infinite loop PCD_Reset()

commited by @psgreco

src/MFRC522.cpp

@@ -232,11 +232,11 @@ void MFRC522::PCD_Reset() {
 	// The datasheet does not mention how long the SoftRest command takes to complete.
 	// But the MFRC522 might have been in soft power-down mode (triggered by bit 4 of CommandReg) 
 	// Section 8.8.2 in the datasheet says the oscillator start-up time is the start up time of the crystal + 37,74μs. Let us be generous: 50ms.
-	delay(50);
-	// Wait for the PowerDown bit in CommandReg to be cleared
-	while (PCD_ReadRegister(CommandReg) & (1<<4)) {
-		// PCD still restarting - unlikely after waiting 50ms, but better safe than sorry.
-	}
+	uint8_t count = 0;
+	do {
+		// Wait for the PowerDown bit in CommandReg to be cleared (max 3x50ms)
+		delay(50);
+	} while ((PCD_ReadRegister(CommandReg) & (1 << 4)) && (++count) < 3);
 } // End PCD_Reset()
 
 /**