rng-tools: Fix crazy defaults

Since commit [f1dc9ac rng-tools: Fix crazy defaults] fixed
init based on sysvinit, this fix rngd.service based on systemd.

(From OE-Core rev: b1980460839baa04d10866877cbfe31ca8093ff3)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/rng-tools/rng-tools/rngd.service

@@ -5,7 +5,7 @@ After=systemd-udev-settle.service
 Before=sysinit.target
 
 [Service]
-ExecStart=@SBINDIR@/rngd -f -r /dev/urandom
+ExecStart=@SBINDIR@/rngd -f -r /dev/hwrng
 SuccessExitStatus=66
 
 [Install]