sh: push-switch: Correct license string.

This was accidentally set as "GPLv2", whereas the kernel expects v2
to be written "GPL v2", this caused complaints regarding the use
of the platform device APIs when built as a module.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/drivers/push-switch.c

@@ -138,4 +138,4 @@ module_exit(switch_exit);
 
 MODULE_VERSION(DRV_VERSION);
 MODULE_AUTHOR("Paul Mundt");
-MODULE_LICENSE("GPLv2");
+MODULE_LICENSE("GPL v2");