commit 9051bd39 upstream.

A new Micron drive was just announced, once again recycling the first
part of the model string. Add an underscore to the M510/M550 pattern to
avoid picking up the new DC drive.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>