cuse: fix uninitialized variable warnings

Fix the following compiler warnings:

fs/fuse/cuse.c: In function 'cuse_process_init_reply':
fs/fuse/cuse.c:288:24: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]
fs/fuse/cuse.c:272:14: note: 'val' was declared here
fs/fuse/cuse.c:284:10: warning: 'key' may be used uninitialized in this function [-Wmaybe-uninitialized]
fs/fuse/cuse.c:272:8: note: 'key' was declared here

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>