drv/sdc: Implement "SDC@" as a BLK@ word

"0 LIST" in the RC2014 emulator w/ SD card works!

drv/sdc.fs

@@ -156,15 +156,20 @@
     0
 ;
 
-( dstaddr blkno -- f )
-: SDC@
+: _err
+    _desel
+    ABORT" SDC error"
+;
+
+( dstaddr blkno -- )
+: _sdc@
     _sel
     0x51    ( CMD17 )
     0 ROT   ( a cmd 0 blkno )
     _cmd
-    IF _desel 0 EXIT THEN
+    IF _err THEN
     _wait
-    0xfe = NOT IF _desel 0 EXIT THEN
+    0xfe = NOT IF _err THEN
     0 SWAP           ( crc a )
     512 0 DO         ( crc a )
         DUP          ( crc a a )
@@ -180,5 +185,12 @@
     _idle +          ( crc2 )
     _wait DROP
     _desel
-    =   ( success if crc1 == crc2 )
+    = NOT IF _err THEN
+;
+
+: SDC@
+    2 * DUP BLK( SWAP    ( b a b )
+    _sdc@
+    1+ BLK( 512 + SWAP
+    _sdc@
 ;