[media] saa7115: make multi-line comments compliant with CodingStyle

changeset 2ccf12af did a crappy job when added multi-line comment lines,
violating CodingStyle.

Change the comments added there to fulfill CodingStyle, and document
the platform_data using Documentation/kernel-doc-nano-HOWTO.txt.

Cc: Jon Arne Jørgensen <jonarne@jonarne.no>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>