qtnfmac: fix uninitialized return code in ret

The return value ret is unitialized and garbage is being returned
for the three different error conditions when setting up the PCIe
BARs. Fix this by initializing ret to  -ENOMEM to indicate that
the BARs failed to be setup correctly.

Detected by CoverityScan, CID#1437563 ("Unitialized scalar variable")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>