ACPI / proc: Include appropriate header file in proc.c

Include appropriate header file internal.h in proc.c because function
acpi_sleep_proc_init() has its prototype declaration in internal.h.

This eliminates the following warning in proc.c:
drivers/acpi/proc.c:148:12: warning: no previous prototype for ‘acpi_sleep_proc_init’ [-Wmissing-prototypes]
Signed-off-by: NRashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/proc.c

@@ -7,6 +7,7 @@
 #include <asm/uaccess.h>
 
 #include "sleep.h"
+#include "internal.h"
 
 #define _COMPONENT		ACPI_SYSTEM_COMPONENT