Minor documentation and formatting fixes #799

I noticed a few small typos, documentation inconsistencies, and formatting issues.
These are all minor cleanup items, but fixing them would improve consistency and readability:

• ltc_pkcs_1_pss_encode_mgf1.c:72: remove the unnecessary blank line
• hmac_init.c:67: remove extra spaces
• hash_memory.c: hash_descriptor[hash].hashsize is accessed multiple times. It could be stored in a local variable (like in hmac_done.c) after validating the hash, and then reused throughout the function:

unsigned long hashsize;

/* ... */

if ((err = hash_is_valid(hash)) != CRYPT_OK) {
    return err;
}

hashsize = hash_descriptor[hash].hashsize;

• der_decode_choice.c:111+112: align the calculation lines
• der_decode_integer.c:75: remove the unnecessary blank line
• der_decode_short_integer.c:62: remove the unnecessary blank line
• der_decode_utctime.c:74-81: align the comment
• der_decode_generalizedtime.c:91-98: align the comment
• s_der_decode_sequence_flexi.c: The XMALLOC, XCALLOC and XREALLOC calls use a code style that differs from the rest of the codebase. I would prefer to write them as separate assignment and NULL-check statements, for example:

             l->data = XMALLOC(len);
             if(l->data == NULL) {
                err = CRYPT_MEM;
                goto error;
             }

instead of:

             if ((l->data = XMALLOC(len)) == NULL) {
                err = CRYPT_MEM;
                goto error;
             }