net: bcmasp: Prevent array undereflow in bcmasp_netfilt_get_init()

The "loc" value comes from the user and it can be negative leading to an
an array underflow when we check "priv->net_filters[loc].claimed".  Fix
this by changing the type to u32.

Fixes: c5d511c4 ("net: bcmasp: Add support for wake on net filters")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Justin Chen <justin.chen@broadcom.com>
Link: https://lore.kernel.org/r/b3b47b25-01fc-4d9f-a6c3-e037ad4d71d7@moroto.mountain


Signed-off-by: Jakub Kicinski <kuba@kernel.org>