iproc_i2c_rd_reg() and iproc_i2c_wr_reg() are called from both
interrupt context (e.g. bcm_iproc_i2c_isr) and process context
(e.g. bcm_iproc_i2c_suspend). Therefore, interrupts should be
disabled to avoid potential deadlock. To prevent this scenario,
use spin_lock_irqsave().

Fixes: 9a103872 ("i2c: iproc: add NIC I2C support")
Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
Acked-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>