ipq-wifi: Fix suffix for Plasma Cloud PA1200 QCA4019 board-2.bin

The Makefile is rejecting all files with for a given prefix (here
"board-plasmacloud_pa1200") when it didn't match a known suffix. Instead it
stops the build with an error like:

  Makefile:135: *** Unrecognized board-file suffix '.ipq4019' for 'board-plasmacloud_pa1200.ipq4019'. Stop.

The correct suffix for the QCA4019/hw1.0 is qca4019 and not ipq4019.

Fixes: ea5bb6bb ("ipq40xx: add support for Plasma Cloud PA1200")
Signed-off-by: Sven Eckelmann <sven@narfation.org>