relp: fix build against upcoming `gcc-14` (`-Werror=calloc-transposed…

[kraj]

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…-args`)

gcc-14 added a new -Wcalloc-transposed-args warning recently. It detected minor infelicity in calloc() API usage

Fixes ../../git/src/relp.c: In function 'addToEpollSet': ../../git/src/relp.c:101:39: error: 'calloc' sizes specified with 'sizeof' in the earlier argument and not in the later argument [-Werror=calloc-transposed-args] 101 | CHKmalloc(epd = calloc(sizeof(epolld_t), 1)); | ^~~~~~~~