Add missing volatile to status flags in sd_diskio.c (#678)

To prevent the while loops from being optimized into
very long loops that always wait for the timeout.

Author: TheSlowGrowth

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Bug Fixes
+
+- SDMMC: fix an issue where status flags were optimized out, resulting in very long while loops
+
 ## v8.0.0
 
 ### Features

src/util/sd_diskio.c

@@ -57,8 +57,8 @@
 /* Disk status */
 static volatile DSTATUS Stat = STA_NOINIT;
 //static volatile  UINT  WriteStatus = 0, ReadStatus = 0;
-static uint32_t WriteStatus = 0;
-static uint32_t ReadStatus  = 0;
+static volatile uint32_t WriteStatus = 0;
+static volatile uint32_t ReadStatus  = 0;
 /* Private function prototypes -----------------------------------------------*/
 static DSTATUS SD_CheckStatus(BYTE lun);
 DSTATUS        SD_initialize(BYTE);