gralloc: don't initialize reserved_proc

gralloc: don't initialize reserved_proc

gcc supports designated initializers in C++ mode as an extension, but
*only* when all of the specified fields are at the beginning of the
struct.  Hence initializing reserved_proc breaks compilation when new
procs are added.

Initializing reserved_proc makes a (spurious) warning go away, so
instead directly suppress that warning.

Change-Id: I279b7070b1aa7068c23fb59422589ff31980432d
Signed-off-by: Greg Hackmann <ghackmann@google.com>