PCI: altera: Fix bool initialization in tlp_read_packet()

Bool variables should be initialized only through true and false
values; update tlp_read_packet() code to comply.

Detected using the Coccinelle tool.

Fixes: eaa6111b ("PCI: altera: Add Altera PCIe host controller driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Ley Foon Tan <ley.foon.tan@intel.com>