x86: unify dma_mapping_error

We provide a map_error function in pci-base_32.c to make
sure i386 keeps with the same behaviour it used to.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>