While I was investigating CID 1194192 related with a resource leak on mrp memory

While I was investigating CID 1194192 related with a resource leak on mrp memory
allocation, I could identify that actually we use this pointer on pci_emul.c as
well as on vga.c source file.

I have reworked the logic here to make it more readable and also add a warn to
explicit show the function where the memory allocation error could happen,
also sort headers.

Also CID 1194192 was marked as "Intentional".

Obtained from:	TrueOS
MFC after:	4 weeks.
Sponsored by:	iXsystems Inc.