host tests: Fix test that accessed unspecified memory

Depending on compiler optimization and version
ble_att_svr_test_read_mult() could rise error:

In function ‘memcpy’,
    inlined from ‘TEST_CASE_ble_att_svr_test_read_mult’ at repos/apache-mynewt-nimble/nimble/host/test/src/ble_att_svr_test.c:1027:5:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:29:10: error: ‘__builtin_memcpy’ forming offset [18, 19] is out of the bounds [0, 18] of object ‘({anonymous})’ with type ‘uint8_t[18]’ {aka ‘unsigned char[18]’} [-Werror=array-bounds=]
   29 |   return __builtin___memcpy_chk (__dest, __src, __len,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   30 |                                  __glibc_objsize0 (__dest));

array was clearly to short for memcpy and later data with 20
bytes had 2 unspecified values at the end

Signed-off-by: Jerzy Kasenberg <[email protected]>

Author: kasjer

nimble/host/test/src/ble_att_svr_test.c

@@ -1026,7 +1026,7 @@ TEST_CASE_SELF(ble_att_svr_test_read_mult)
     attrs[1].value_len = 20;
     memcpy(attrs[1].value,
            ((uint8_t[]){
-                22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39
+                20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39
            }),
            attrs[1].value_len);
     ble_att_svr_test_attr_r_2_len = attrs[1].value_len;