Input: twl6040-vibra - fix compiler warning

Fix warning from Geert's build summary emails by changing "if" to
"ifdef". Thsi should fix the following:

drivers/input/misc/twl6040-vibra.c:231:5: warning: "CONFIG_PM_SLEEP" is not defined

Builds cleanly with CONFIG_PM_SLEEP enabled or disabled.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>