FAT: Fixed volume count check when formatted without MBR

This saves 64 blocks (32KB when used with 512B blocks) and drops
the minimum storage size from 64KB to 32KB.

Author: geky

features/filesystem/fat/ChaN/ff.cpp

@@ -4123,7 +4123,7 @@ FRESULT f_mkfs (
 		n_vol = LD_DWORD(tbl + 12);	/* Volume size */
 	} else {
 		/* Create a partition in this function */
-		if (disk_ioctl(pdrv, GET_SECTOR_COUNT, &n_vol) != RES_OK || n_vol < 128)
+		if (disk_ioctl(pdrv, GET_SECTOR_COUNT, &n_vol) != RES_OK || n_vol < ((sfd) ? 64 : 128))
 			return FR_DISK_ERR;
 		b_vol = (sfd) ? 0 : 63;		/* Volume start sector */
 		n_vol -= b_vol;				/* Volume size */