libbb: Converted safe_read to safe_write format

Changed safe_read to be symmetrical to safe_write, it shall
never return EINTR because it calls read multiple times,
the error is considered transient.

function                                             old     new   delta
safe_read                                             44      57     +13

Signed-off-by: Martin Lewis <martin.lewis.x84@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/read.c

@@ -12,9 +12,17 @@ ssize_t FAST_FUNC safe_read(int fd, void *buf, size_t count)
 {
 	ssize_t n;
 
-	do {
+	for (;;) {
 		n = read(fd, buf, count);
-	} while (n < 0 && errno == EINTR);
+		if (n >= 0 || errno != EINTR)
+			break;
+		/* Some callers set errno=0, are upset when they see EINTR.
+		 * Returning EINTR is wrong since we retry read(),
+		 * the "error" was transient.
+		 */
+		errno = 0;
+		/* repeat the read() */
+	}
 
 	return n;
 }