Replace "struct list_head head = LIST_HEAD_INIT(head)" with
"LIST_HEAD(head)" to simplify the code.

LIST_HEAD() helps to clean up the code "struct list_head vudc_devices =",
only to care about the variable 'vudc_devices'.
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Cai Huoqing <cai.huoqing@linux.dev>
Link: https://lore.kernel.org/r/20220211012807.7415-1-cai.huoqing@linux.devSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>