seedrng: use predefined strings where possible

- Use predefined strings where possible.
- Open /dev/random with O_RDONLY for ioctl().

function                                             old     new   delta
seed_from_file_if_exists                             413     410      -3
.rodata                                           108407  108350     -57
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-60)             Total: -60 bytes
   text	   data	    bss	    dec	    hex	filename
 975979	   4227	   1816	 982022	  efc06	busybox_old
 975919	   4227	   1816	 981962	  efbca	busybox_unstripped

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
1 file changed