platform/x86: dell-laptop: make some local functions static
Fixes the following sparse warnings:
drivers/platform/x86/dell-laptop.c:289:6: warning:
symbol 'dell_set_arguments' was not declared. Should it be static?
drivers/platform/x86/dell-laptop.c:298:5: warning:
symbol 'dell_send_request' was not declared. Should it be static?