ata: libata-eh: Clarify ata_eh_qc_retry() behavior at call site

While the function documentation for ata_eh_qc_retry() is clear,
from simply reading the single function that calls ata_eh_qc_retry(),
it is not clear that ata_eh_qc_retry() might not retry the command.

Add a comment in the single function that calls ata_eh_qc_retry() to
clarify the behavior.

[Damien] Added curly braces to "if () else" with multi-line comment.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>