Fix checking fat32 cluster size.

This fixes the cluster size tests in the FAT32 file system.
The current implementation of VFAT support doesn't work if the
referred cluster has an offset > 16bit representation, causing
"fatload" and "fatls" commands etc. to fail.

Signed-off-by: michael trimarchi <trimarchi@gandalf.sssup.it>
diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index c1e5741..49c78ed 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -352,7 +352,7 @@
 			newclust = get_fatent(mydata, endclust);
 			if((newclust -1)!=endclust)
 				goto getit;
-			if (newclust <= 0x0001 || newclust >= 0xfff0) {
+			if (CHECK_CLUST(newclust, mydata->fatsize)) {
 				FAT_DPRINT("curclust: 0x%x\n", newclust);
 				FAT_DPRINT("Invalid FAT entry\n");
 				return gotsize;
@@ -387,7 +387,7 @@
 		filesize -= actsize;
 		buffer += actsize;
 		curclust = get_fatent(mydata, endclust);
-		if (curclust <= 0x0001 || curclust >= 0xfff0) {
+		if (CHECK_CLUST(curclust, mydata->fatsize)) {
 			FAT_DPRINT("curclust: 0x%x\n", curclust);
 			FAT_ERROR("Invalid FAT entry\n");
 			return gotsize;
@@ -459,7 +459,7 @@
 
 		slotptr--;
 		curclust = get_fatent(mydata, curclust);
-		if (curclust <= 0x0001 || curclust >= 0xfff0) {
+		if (CHECK_CLUST(curclust, mydata->fatsize)) {
 			FAT_DPRINT("curclust: 0x%x\n", curclust);
 			FAT_ERROR("Invalid FAT entry\n");
 			return -1;
@@ -652,7 +652,7 @@
 	    return retdent;
 	}
 	curclust = get_fatent (mydata, curclust);
-	if (curclust <= 0x0001 || curclust >= 0xfff0) {
+	if (CHECK_CLUST(curclust, mydata->fatsize)) {
 	    FAT_DPRINT ("curclust: 0x%x\n", curclust);
 	    FAT_ERROR ("Invalid FAT entry\n");
 	    return NULL;