net: bridge: remove redundant check to see if err is set

The error check on err is redundant as it is being checked
previously each time it has been updated.  Remove this redundant
check.

Detected with CoverityScan, CID#140030("Logically dead code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>