tpm: Convert warn to dbg in tpm2_start_auth_session()

[ Upstream commit 6359691b4fbcaf3ed86f53043a1f7c6cc54c09be ]

TPM2 sessions have been flushed lazily since commit df745e2509 ("tpm:
Lazily flush the auth session").  If /dev/tpm{rm}0 is not accessed
in-between two in-kernel calls, it is possible that a TPM2 session is
re-started before the previous one has been completed.

This causes a spurios warning in a legit run-time condition, which is also
correctly addressed with a fast return path:

[    2.944047] tpm tpm0: auth session is active

Address the issue by changing dev_warn_once() call to a dev_dbg_once()
call.

[jarkko: Rewrote the commit message, and instead of dropping converted
 to a debug message.]
Signed-off-by: Jonathan McDowell <noodles@meta.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/char/tpm/tpm2-sessions.c

@@ -974,7 +974,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	int rc;
 
 	if (chip->auth) {
-		dev_warn_once(&chip->dev, "auth session is active\n");
+		dev_dbg_once(&chip->dev, "auth session is active\n");
 		return 0;
 	}