The same checks are repeated in three places to decide whether to use
hwrng. Consolidate these into a helper.
Also this fixes a case that one of them was missing a check in the
cleanup path.
Fixes: 554b841d47 ("tpm: Disable RNG for all AMD fTPMs")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>