i2c: octeon: Fix i2c fail problem when a process is terminated by a signal

I've been debugging the abnormal operation of i2c on octeon. If a process is
terminated by signal in the middle of i2c operation, next i2c read operation
which is done by another process was failed. So i changed to ignore signal in
the middle of i2c operation. After that the problem was not reproduced.

Signed-off-by: Eunbong Song <eunb.song@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>