fbcon: Fix memory leak in con2fb_release_oldinfo()

kmemleak reported a memory leak as below.

unreferenced object 0xffff8800dab6d8d8 (size 96):
  comm "swapper/0", pid 1, jiffies 4294877598 (age 38.483s)
  hex dump (first 32 bytes):
    00 00 00 00 00 01 00 00 08 00 00 00 10 00 00 00  ................
    07 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff814e8f2e>] kmemleak_alloc+0x4e/0xb0
    [<ffffffff811a0600>] __kmalloc+0x280/0x320
    [<ffffffff81309b61>] soft_cursor+0x231/0x290
    [<ffffffff81309393>] bit_cursor+0x613/0x650
    [<ffffffff8130556b>] fbcon_cursor+0x13b/0x1c0
    [<ffffffff813755f8>] hide_cursor+0x28/0xa0
    [<ffffffff81376e98>] redraw_screen+0x168/0x240
    [<ffffffff81303891>] fbcon_prepare_logo+0x381/0x420
    [<ffffffff81303c7e>] fbcon_init+0x34e/0x590
    [<ffffffff81375828>] visual_init+0xb8/0x120
    [<ffffffff81377c93>] do_bind_con_driver+0x163/0x380
    [<ffffffff81378494>] do_take_over_console+0x114/0x1c0
    [<ffffffff81303f23>] do_fbcon_takeover+0x63/0xd0
    [<ffffffff813086dd>] fbcon_event_notify+0x68d/0x7e0
    [<ffffffff814ff7ac>] notifier_call_chain+0x4c/0x70
    [<ffffffff8108c85d>] __blocking_notifier_call_chain+0x4d/0x70

This memory leak cause is, fbcon_ops's cursor_src is allocated in
soft_cursor() but not released in con2fb_release_oldinfo().
so, cursor_src is needed to be released when oldinfo is going to be
released.

Signed-off-by: Masami Ichikawa <masami256@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>