[media] hdpvr: Refactoring for hdpvr_read()

Let us return directly if the element "status" of the variable "buf"
indicates "BUFSTAT_READY".
A check repetition can be excluded for the variable "ret" at the end then.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>