Fix a signed shift overflow in vpx_rb_read_inv_signed_literal.

Found with clang -fsanitize=integer

Change-Id: I17cb2166c06ff463abfaf9b0e6bc749d0d6fdf94

vpx_dsp/bitreader_buffer.c

@@ -45,7 +45,7 @@ int vpx_rb_read_inv_signed_literal(struct vpx_read_bit_buffer *rb,
                                    int bits) {
 #if CONFIG_MISC_FIXES
   const int nbits = sizeof(unsigned) * 8 - bits - 1;
-  const unsigned value = vpx_rb_read_literal(rb, bits + 1) << nbits;
+  const unsigned value = (unsigned)vpx_rb_read_literal(rb, bits + 1) << nbits;
   return ((int) value) >> nbits;
 #else
   return vpx_rb_read_signed_literal(rb, bits);