tfm: mbedtls: Fix build warning

/__w/zephyr/modules/crypto/mbedtls/library/aes.c:307:23: warning:
'RT0' defined but not used [-Wunused-const-variable=]
307 | static const uint32_t RT0[256] = { RT };
      |                       ^~~
/__w/zephyr/modules/crypto/mbedtls/library/aes.c:200:28: warning:
'RSb' defined but not used [-Wunused-const-variable=]
  200 | static const unsigned char RSb[256] =
      |                            ^~~
[360/437] Building C object

Fixes #51025

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>