Fixes the warnings related to the linkage

To reproduce the issue just run:

      ~/h/o/a/Lyra git:master ❯❯❯ make
      cc Lyra.c Sponge.c Main.c -o Lyra -std=c99 -Wall -pedantic -O3 -lm
      Sponge.c:38:37: warning: static variable 'blake2b_IV' is used in an inline function with external linkage [-Wstatic-in-inline]
          memcpy(state + BLOCK_LEN_INT64, blake2b_IV,   BLOCK_LEN_BYTES);
                                          ^
      /usr/include/secure/_string.h:65:33: note: expanded from macro 'memcpy'
        __builtin___memcpy_chk (dest, src, len, __darwin_obsz0 (dest))
                                      ^
      ./Sponge.h:60:1: note: use 'static' to give inline function 'initState' internal linkage
      void initState(uint64_t state[/*16*/]);
      ^
      static
      ./Sponge.h:22:23: note: 'blake2b_IV' declared here
      static const uint64_t blake2b_IV[8] =

I hope it helps