wlcore: enter elp in force ps mode in 5ms

It is requiered to enter sleep mode with smaller delay in forced PS mode.
This fixes issue of testing force PS mode during VoIP traffic where packets
are sent every 20ms. Chip never enters ps mode with default 30 ms delay
in such test.

Signed-off-by: Igal Chernobelsky <igalc@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>