eeepc-wmi: Build fix

-tip testing found:

eeepc-wmi.c:(.text+0x36673c): undefined reference to `sparse_keymap_report_event'
drivers/built-in.o: In function `eeepc_wmi_init':
eeepc-wmi.c:(.init.text+0x19cd0): undefined reference to `sparse_keymap_setup'
eeepc-wmi.c:(.init.text+0x19cf0): undefined reference to `sparse_keymap_free'
eeepc-wmi.c:(.init.text+0x19d0b): undefined reference to `sparse_keymap_free'
drivers/built-in.o: In function `eeepc_wmi_exit':
eeepc-wmi.c:(.exit.text+0x2e87): undefined reference to `sparse_keymap_free'

To fix this select INPUT_SPARSEKMAP, like the ASUS driver does.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Matthew Garrett <mjg@redhat.com>