One ide command for nsector_per_block generates nsector_per_block int…

…errupts,

instead of 1.   ideintr() should wait for nsector_per_block interrupts before
waking up the reader; now it wakes up the reader after 1 interrupt, which
apparently means that the first sector is available of the command instead of all.
For now keep BSIZE to 512.

fs.h

@@ -9,7 +9,7 @@
 // Then sb.nlog log blocks.
 
 #define ROOTINO 1  // root i-number
-#define BSIZE 1024  // block size
+#define BSIZE 512  // block size
 
 // File system super block
 struct superblock {