MIPS: PCI: fix pcibios_map_irq section mismatch

Drop  the __init from pcibios_map_irq() to make this section mis-
match go away:

WARNING: vmlinux.o(.text+0x56acd4): Section mismatch in reference from the function pcibios_scanbus() to the function .init.text:pcibios_map_irq()
The function pcibios_scanbus() references
the function __init pcibios_map_irq().
This is often because pcibios_scanbus lacks a __init
annotation or the annotation of pcibios_map_irq is wrong.

Run-Tested only on Alchemy.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17267/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>