wlcore: decrease elp timeout

The current elp timeout (the same as the dynamic
ps timeout - 1500ms) is too high. Usually,
wl1271_ps_elp_sleep() get called right after tx/rx,
which is fine, but some command might get sent
even when there is no traffic (e.g. ht changes
triggered by beacon frames), and leaving the
device awake for 1500ms in this case is redundant.

Use a timeout of 30ms.
The fw won't enter elp anyway before the dynamic-ps
timeout was expired as well (and it entered ps
successfully).

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <luca@coelho.fi>