ata: libata-eh: Improve reset error messages

Some drives are really slow to spinup on resume, resulting is a very
slow response to COMRESET and to error messages such as:

ata1: COMRESET failed (errno=-16)
ata1: link is slow to respond, please be patient (ready=0)
ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
ata1.00: configured for UDMA/133

Given that the slowness of the response is indicated with the message
"link is slow to respond..." and that resets are retried until the
device is detected as online after up to 1min (ata_eh_reset_timeouts),
there is no point in printing the "COMRESET failed" error message. Let's
not scare the user with non fatal errors and only warn about reset
failures in ata_eh_reset() when all reset retries have been exhausted.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>