media: atomisp-gc2235: drop an unused var

Fix this clang Werror with W=1:

drivers/staging/media/atomisp/i2c/atomisp-gc2235.c:573:6: error: variable 'ret' set but not used [-Werror,-Wunused-but-set-variable]
        int ret = -1;
            ^

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>