alsdec: Fix out of ltp_gain_values read.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Justin Ruggles <justin.ruggles@gmail.com>
(cherry picked from commit 97f0efbfb8)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/alsdec.c

@@ -741,7 +741,7 @@ static int read_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
             bd->ltp_gain[0]   = decode_rice(gb, 1) << 3;
             bd->ltp_gain[1]   = decode_rice(gb, 2) << 3;
 
-            r                 = get_unary(gb, 0, 4);
+            r                 = get_unary(gb, 0, 3);
             c                 = get_bits(gb, 2);
             bd->ltp_gain[2]   = ltp_gain_values[r][c];