zstd: use U16 data type for rankPos

rankPos structure variables value can not be more than 512.  So it can
easily be declared as U16 rather than U32.

It will reduce stack usage of HUF_sort from 256 bytes to 128 bytes

original:
e92ddbf0        push    {r4, r5, r6, r7, r8, r9, fp, ip, lr, pc}
e24cb004        sub     fp, ip, #4
e24ddc01        sub     sp, sp, torvalds#256    ; 0x100

changed:
e92ddbf0        push    {r4, r5, r6, r7, r8, r9, fp, ip, lr, pc}
e24cb004        sub     fp, ip, #4
e24dd080        sub     sp, sp, torvalds#128    ; 0x80

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Maninder Singh <[email protected]>
Signed-off-by: Vaneet Narang <[email protected]>
Cc: Amit Sahrawat <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>

lib/zstd/huf_compress.c

@@ -382,8 +382,8 @@ static U32 HUF_setMaxHeight(nodeElt *huffNode, U32 lastNonNull, U32 maxNbBits)
 }
 
 typedef struct {
-	U32 base;
-	U32 curr;
+	U16 base;
+	U16 curr;
 } rankPos;
 
 static void HUF_sort(nodeElt *huffNode, const U32 *count, U32 maxSymbolValue)