ARM: OMAP: OTG integration: fix compiler warning

Tony reported the following compile warning after commit
eeb3711b ("ARM: OMAP2+: clean up some
cppcheck warnings"):

arch/arm/plat-omap/usb.c: In function 'omap_otg_init':
arch/arm/plat-omap/usb.c:40: warning: unused variable 'status'

This happens if CONFIG_ARCH_OMAP_OTG is set but
CONFIG_USB_GADGET_OMAP, CONFIG_USB_OHCI_HCD,
CONFIG_USB_OHCI_HCD_MODULE, and CONFIG_USB_OTG are all unset.

Fix by localizing the status variable to the blocks that use it.

Compile-tested only, with omap2plus_defconfig and omap2plus_defconfig
with CONFIG_USB_OHCI_HCD and CONFIG_USB_OTG enabled.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>