Before this commit, each rpmsgdev server only manages one file
no matter how many times the client opened.
It can't work fine with some complex drivers, such as input driver
(keyboard, touchscreen and button), because input driver will alloc
a new private open structure for every open operation to make sure
all the applications don't miss data when input driver is used by
multiple applications.
This commit solves this problem by making the files in server and
client be one-to-one.
Signed-off-by: wangbowen6 <wangbowen6@xiaomi.com>
