staging: rtl8192u: ieee80211: remove set but not used variable 'data_len'

staging: rtl8192u: ieee80211: remove set but not used variable 'data_len'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c:
 In function ieee80211_ccmp_encrypt:
drivers/staging/rtl8192u/ieee80211/ieee80211_crypt_ccmp.c:162:6:
 warning: variable data_len set but not used [-Wunused-but-set-variable]

It is not used since commit eb0e7bf3ca94 ("staging:
rtl8192u: ieee80211: ieee80211_crypt_ccmp.c: Use crypto API ccm(aes)")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20190821122250.71404-1-yuehaibing@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>