ACPI Thinkpad: We must always call va_end() after va_start() but do not do so in thinkpad_acpi.c::acpi_evalf()

Hi,

In drivers/platform/x86/thinkpad_acpi.c::acpi_evalf() we don't always call
va_end() after va_start(). This patch corrects that.
Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Matthew Garrett <mjg@redhat.com>