[MIPS] Drop __devinit tag from allocate_irqno() and free_irqno()
This fix these warnings:
WARNING: arch/mips/kernel/built-in.o - Section mismatch: reference to .init.text:free_irqno from __ksymtab_gpl between '__ksymtab_free_irqno' (at offset 0x0) and '__ksymtab_allocate_irqno'
WARNING: arch/mips/kernel/built-in.o - Section mismatch: reference to .init.text:allocate_irqno from __ksymtab_gpl after '__ksymtab_allocate_irqno' (at offset 0x8)