cp: Remove useless ssize_t cast

Both wcount and wresid are ssize_t so this cast is not needed. Just
remove it so the code is easier to read.

Signed-off-by:	Collin Funk <collin.funk1@gmail.com>
Reviewed by:	emaste, zlei
Pull Request:	#1116

(cherry picked from commit 8b86415)

bin/cp/utils.c

@@ -97,7 +97,7 @@ copy_fallback(int from_fd, int to_fd)
 		wcount = write(to_fd, bufp, wresid);
 		if (wcount <= 0)
 			break;
-		if (wcount >= (ssize_t)wresid)
+		if (wcount >= wresid)
 			break;
 	}
 	return (wcount < 0 ? wcount : rcount);