scsi: storvsc: Log TEST_UNIT_READY errors as warnings

Commit 08f76547 ("scsi: storvsc: Update error logging") added more
robust logging of errors, particularly those reported as Hyper-V
errors. But this change produces extra logging noise in that
TEST_UNIT_READY may report errors during the normal course of detecting
device adds and removes.

Fix this by logging TEST_UNIT_READY errors as warnings, so that log lines
are produced only if the storvsc log level is changed to WARN level on the
kernel boot line.

Link: https://lore.kernel.org/r/1628269970-87876-1-git-send-email-mikelley@microsoft.com
Fixes: 08f76547

 ("scsi: storvsc: Update error logging")
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>