i2c: bcm-iproc: Fix bcm_iproc_i2c_isr deadlock issue

i2c: bcm-iproc: Fix bcm_iproc_i2c_isr deadlock issue

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: 9a1038728037 ("i2c: iproc: add NIC I2C support")
Signed-off-by: Chengfeng Ye <[email protected]>
Acked-by: Ray Jui <[email protected]>
Reviewed-by: Andi Shyti <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>