[sr-dev] [kamailio/kamailio] lib/srutils: fix gcc warning GH#612 (#626)

sha256.c: In function 'sr_SHA256_Final': sha256.c:613:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] *(sha2_word64*)&context->buffer[SHA256_SHORT_BLOCK_LENGTH] = context->bitcount; ^ sha256.c: In function 'SHA512_Last': sha256.c:930:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] *(sha2_word64*)&context->buffer[SHA512_SHORT_BLOCK_LENGTH] = context->bitcount[1]; ^ sha256.c:931:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] *(sha2_word64*)&context->buffer[SHA512_SHORT_BLOCK_LENGTH+8] = context->bitcount[0]; ^