usb: otg: isp1301_omap: resolve unused variable warning from gcc

Resolve this build warning:

drivers/usb/otg/isp1301_omap.c: In function 'isp1301_set_peripheral':
drivers/usb/otg/isp1301_omap.c:1340:6: warning: unused variable 'l'

This shows up when building with the 'omap1_defconfig' and
'5912osk_testconfig' configs from git://git.pwsan.com/omap_kconfigs.

Compile-tested only.

Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Felipe Balbi <balbi@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>