Fix SDSUPPORT (and indentation)

Based on https://github.com/MarlinFirmware/Marlin/issues/8746#issuecomment-368471901 by @benlye

Marlin/src/sd/Sd2Card.cpp

@@ -250,7 +250,7 @@ bool Sd2Card::init(uint8_t sckRateID, pin_t chipSelectPin) {
   #endif
 
   // set pin modes
-//todo: should use chipSelectPin ?
+  pinMode(chipSelectPin_, OUTPUT); // Solution for #8746 by @benlye
   spiBegin();
 
   // set SCK rate for initialization commands
@@ -273,13 +273,13 @@ bool Sd2Card::init(uint8_t sckRateID, pin_t chipSelectPin) {
   #endif
 
   // check SD version
-  while (1) {
+  for (;;) {
     if (cardCommand(CMD8, 0x1AA) == (R1_ILLEGAL_COMMAND | R1_IDLE_STATE)) {
       type(SD_CARD_TYPE_SD1);
       break;
     }
 
-    // only need last byte of r7 response
+    // Get the last byte of r7 response
     for (uint8_t i = 0; i < 4; i++) status_ = spiRec();
     if (status_ == 0xAA) {
       type(SD_CARD_TYPE_SD2);