hash: fix compiler warning on ARM

* cipher/md.c (md_open, md_copy): Cast 'char *' to ctx through
'void *'.
* cipher/md4.c (md4_final): Use buf_put_* helper instead of
converting 'char *' to 'u32 *'.
* cipher/md5.c (md5_final): Ditto.
* cipher/rmd160.c (_gcry_rmd160_mixblock, rmd160_final): Ditto.
* cipher/sha1.c (sha1_final): Ditto.
* cipher/sha256.c (sha256_final): Ditto.
* cipher/sha512.c (sha512_final): Ditto.
* cipher/tiger.c (tiger_final): Ditto.

Patch fixes 'cast increases required alignment' warnings seen on GCC:

md.c: In function 'md_open':
md.c:318:23: warning: cast increases required alignment of target type [-Wcast-align]

hd->ctx = ctx = (struct gcry_md_context *) ((char *) hd + n);
                ^

md.c: In function 'md_copy':
md.c:491:22: warning: cast increases required alignment of target type [-Wcast-align]

bhd->ctx = b = (struct gcry_md_context *) ((char *) bhd + n);
               ^

md4.c: In function 'md4_final':
md4.c:258:20: warning: cast increases required alignment of target type [-Wcast-align]
#define X(a) do { *(u32*)p = le_bswap32((*hd).a) ; p += 4; } while(0)

^

md4.c:259:3: note: in expansion of macro 'X'

X(A);
^

md4.c:258:20: warning: cast increases required alignment of target type [-Wcast-align]
#define X(a) do { *(u32*)p = le_bswap32((*hd).a) ; p += 4; } while(0)

^

md4.c:260:3: note: in expansion of macro 'X'

X(B);
^

[removed the rest]

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>