Block: mtip32xx: Improvement in code readability when memdup_user() fails.

There is no need to call kfree() if memdup_user() fails, as no memory
was allocated and the error in the error-valued pointer should be returned.

Signed-off-by: Sachin Shukla <sachin.s5@samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>