NFSD: Remove setting unused variable in nfsd_vfs_read()

Compiling gave me this warning:
fs/nfsd/vfs.c: In function ‘nfsd_vfs_read’:
fs/nfsd/vfs.c:880:16: warning: variable ‘inode’ set but not used
[-Wunused-but-set-variable]

I discovered that a local variable "inode" was being set towards the
beginning of nfsd_vfs_read() and then ignored for the rest of the
function.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>