[media] si2157: add one missing parenthesis
[media] si2157: add one missing parenthesis

Fix following warnings:
si2157_cmd_execute() warn: add some parenthesis here?
si2157_cmd_execute() warn: maybe use && instead of &

Reported-by: Dan Carpenter <ff341aa343d564f9e53e9dcb6996be8c04859a66@oracle.com>
Signed-off-by: Antti Palosaari <293134fe763ce2d9d8609280ea107c73cbd2eb86@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <0cae1d1e981e84d16b82ca3d17be8a7f826608d3@samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs