cifsd: Prefer kernel type 'u16' over 'uint16_t'

Fix a warning from checkpatch.pl --strict:

 CHECK: Prefer kernel type 'u16' over 'uint16_t'
 #112: FILE: server.c:112:
 +       uint16_t command;

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>