toshiba_acpi: make one-bit bitfields unsigned

This doesn't change how the code works, but it silences a Sparse
complaint:
drivers/platform/x86/toshiba_acpi.c:121:37: error: dubious one-bit signed bitfield

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>