media: imx274: document reset delays more clearly

Document the unit to avoid having to look through the code to compute it.
Also clarify that these are min and max values.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>