Input: palmas-pwrbutton - fix typo in the license string

Follow the license string convention indicated in include/linux/module.h
(don't capitalize v).

This fixes following randconfig warning:
FATAL: modpost: GPL-incompatible module palmas-pwrbutton.ko uses GPL-only symbol 'platform_driver_unregister'

Fixes: adff5962fdd2 ("Input: introduce palmas-pwrbutton")
Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/palmas-pwrbutton.c

@@ -328,5 +328,5 @@ module_platform_driver(palmas_pwron_driver);
 
 MODULE_ALIAS("platform:palmas-pwrbutton");
 MODULE_DESCRIPTION("Palmas Power Button");
-MODULE_LICENSE("GPL V2");
+MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Texas Instruments Inc.");