libs: Rename $(SRCS-y) to $(OBJS-y)

libs: Rename $(SRCS-y) to $(OBJS-y)

The only thing done thing done with $(SRCS-y) is to replace ".c" by
".o". It is more useful to collect which object we want to build as
make will figure out how to build it and from which source file.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>