media: flexcop-i2c: Constify struct i2c_algorithm

'struct i2c_algorithm' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increase overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
   6645	    216	     16	   6877	   1add	drivers/media/common/b2c2/flexcop-i2c.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
   6721	    160	     16	   6897	   1af1	drivers/media/common/b2c2/flexcop-i2c.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>