When DEBUG_I2C is open, the following build issue would shows up.

mv_i2c.c: In function 'i2c_transfer':
mv_i2c.c:257: error: 'ISR' undeclared (first use in this function)
mv_i2c.c:257: error: (Each undeclared identifier is reported only once
mv_i2c.c:257: error: for each function it appears in.)

Signed-off-by: Lei Wen <leiwen@marvell.com>