ARM: OMAP: Fix warning in mach-omap1

Fix warning

arch/arm/mach-omap1/pm.c: In function 'omap_pm_init':
arch/arm/mach-omap1/pm.c:765: warning: ignoring return value
of 'subsys_create_file', declared with attribute
warn_unused_result

Signed-off-by: Dirk Behme <dirk.behme_at_gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>