i2c: iproc: fix typo in slave_isr function

Fix typo in bcm_iproc_i2c_slave_isr().

Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Acked-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>