staging: exfat: Clean up return codes - FFS_EOF

Convert FFS_EOF to return 0 for a zero-length read() as per 'man 2 read'.
Signed-off-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20191112021000.42091-4-Valdis.Kletnieks@vt.eduSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/exfat/exfat.h

@@ -217,7 +217,6 @@ static inline u16 get_row_index(u16 i)
 #define FFS_INVALIDFID          8
 #define FFS_NOTOPENED           12
 #define FFS_MAXOPENED           13
-#define FFS_EOF                 15
 #define FFS_ERROR               19
 
 #define NUM_UPCASE              2918

drivers/staging/exfat/exfat_super.c

@@ -723,7 +723,7 @@ static int ffsReadFile(struct inode *inode, struct file_id_t *fid, void *buffer,
 	if (count == 0) {
 		if (rcount)
 			*rcount = 0;
-		ret = FFS_EOF;
+		ret = 0;
 		goto out;
 	}