Fix the following Coverity warning:
CID 244086: Incorrect expression (BAD_COMPARE)
Comparing pointer "ep_bar" against NULL using anything besides == or
is likely to be incorrect.
Fixes: 914026d25848 ("drivers: pci_ep: Introduce UCLASS_PCI_EP uclass")
Signed-off-by: Ramon Fried <rfried.dev@gmail.com>