irqchip.mips-gic: Fix shared interrupt mask writes

The write_gic_smask() & write_gic_rmask() functions take a shared
interrupt number as a parameter, but we're incorrectly providing them a
bitmask with the shared interrupt's bit set. This effectively means that
we mask or unmask the shared interrupt 1<<n rather than shared interrupt
n, and as a result likely drop interrupts.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: 68898c8765f4 ("irqchip: mips-gic: Drop gic_(re)set_mask() functions")
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>