CLEANUP: Apply xalloc_size.cocci

This fixes a few locations with a hardcoded type within `sizeof()`.
diff --git a/src/errors.c b/src/errors.c
index d2eafce..993b6ae 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -126,7 +126,7 @@
 	int ret;
 
 	if (unlikely(b_is_null(&ctx->str))) {
-		area = calloc(USERMSGS_CTX_BUFSIZE, sizeof(char));
+		area = calloc(USERMSGS_CTX_BUFSIZE, sizeof(*area));
 		if (area)
 			ctx->str = b_make(area, USERMSGS_CTX_BUFSIZE, 0, 0);
 	}