power: fix P-state base frequency handling

power: fix P-state base frequency handling

Previous fix for base frequency handling in pstate mode introduced a
couple of issues:

- When base_frequency file does not exist, it simply bails out because
  of what appears to be accidental addition of FOPEN_OR_ERR_RET. This is
  incorrect, as absence of this file is not fatal and is in fact
  expected on kernel versions earlier than 5.3
- When base_frequency file does exist, it gets opened, but never gets
  closed, resulting in a resource leak

Both issues also manifest themselves as Coverity defects (dead code, and
a resource leak), so this fix addresses both.

Coverity issue: 369693, 369694
Bugzilla ID: 668
Fixes: 4db9587bbf72 ("power: check sysfs base frequency")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Reshma Pattan <reshma.pattan@intel.com>