[media] staging/media/davinci_vpfe/dm365_ipipeif.c: fix negativity check

[media] staging/media/davinci_vpfe/dm365_ipipeif.c: fix negativity check

[linux-3.16-rc5/drivers/staging/media/davinci_vpfe/dm365_ipipeif.c:210]:
(style) Checking if unsigned variable 'val' is less than zero.

    val = get_oneshot_mode(ipipeif->input);
    if (val < 0) {
        pr_err("ipipeif: links setup required");
        return -EINVAL;
    }

but

static int get_oneshot_mode(enum ipipeif_input_entity input)

Introduced temporary variable for negativity check.
"val" is afterwards used in a lot of bitwise operations, so changing its type
to signed is not safe, according to CERT C Secure Coding Standards chapter
INT13-C: "Use bitwise operators only on unsigned operands"
https://www.securecoding.cert.org/confluence/display/seccode/INT13-C.+Use+bitwise+operators+only+on+unsigned+operands

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=80521

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>