When gspca_resume is called with a wrong intf value it may pass a useless
ep...

BUG: unable to handle kernel NULL pointer dereference at 0000000000000b0e
[ 2431.484253] IP: [<ffffffffa009a7d4>] gspca_resume+0xd/0x3f [gspca_main]
[ 2431.484270] PGD 3cb60067 PUD 376b7067 PMD 0 
[ 2431.484278] Oops: 0002 [#1] SMP 
[ 2431.484284] last sysfs file: /sys/devices/pci0000:00/0000:00:09.0/host2/target2:0:0/2:0:0:0/block/sda/sda6/stat