usb: musb: omap2430: constify dev_pm_ops structures

Declare dev_pm_ops structures as const as they are only stored in the pm
field of a device_driver structure. This field is of type const, so
dev_pm_ops structures having similar properties can be declared const
too.

Size details after cross compiling the .o file for arm
architecture.

File size before: drivers/usb/musb/omap2430.o
   text	   data	    bss	    dec	    hex	filename
   4141	    400	      8	   4549	   11c5	usb/musb/omap2430.o

File size after: drivers/usb/musb/omap2430.o
   text	   data	    bss	    dec	    hex	filename
   4333	    200	      8	   4541	   11bd	usb/musb/omap2430.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
[b-liu@ti.com: added omap2430 in commit subject prefix]
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>