uinput: fix small leak of screen_info

uinput: fix small leak of screen_info

The following leak is fixed by this patch:
==2648== HEAP SUMMARY:
==2648==     in use at exit: 104,699 bytes in 1,459 blocks
==2648==   total heap usage: 14,177 allocs, 12,718 frees, 1,190,456 bytes allocated
==2648==
==2648== 16 bytes in 1 blocks are definitely lost in loss record 16 of 130
==2648==    at 0x4C29BCF: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==2648==    by 0x10B530: agent_read_complete (vdagentd.c:715)
==2648==    by 0x10E8DC: udscs_read_complete (udscs.c:460)
==2648==    by 0x10EAFC: udscs_do_read (udscs.c:515)
==2648==    by 0x10E490: udscs_client_handle_fds (udscs.c:349)
==2648==    by 0x10E402: udscs_server_handle_fds (udscs.c:337)
==2648==    by 0x10BAB1: main_loop (vdagentd.c:844)
==2648==    by 0x10A3E6: main (vdagentd.c:974)
==2648==
==2648== LEAK SUMMARY:
==2648==    definitely lost: 16 bytes in 1 blocks
==2648==    indirectly lost: 0 bytes in 0 blocks
==2648==      possibly lost: 41,483 bytes in 1,268 blocks
==2648==    still reachable: 63,200 bytes in 190 blocks
==2648==         suppressed: 0 bytes in 0 blocks
==2648== Reachable blocks (those to which a pointer was found) are not shown.
==2648== To see them, rerun with: --leak-check=full --show-leak-kinds=all