wmbattery: avoid truncating ACPI info

wmbattery: avoid truncating ACPI info

Hitherto, the following code has been used to read from ACPI files:

  end = read(fd, buf, sizeof(buf));
  buf[end - 1] = '\0';

This can cause problems, if we read the whole file and there is no new-line:

  $ cat /sys/module/acpi/parameters/acpica_version
  20190816$

In this case, the '\0' will overwrite the last digit, leading to spurious
error reports:

  ACPI subsystem 2019081 too is old, consider upgrading to 20011018.

Instead, read one fewer byte and write the '\0' at the next index:

  end = read(fd, buf, sizeof(buf) - 1);
  buf[end] = '\0';

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>