staging: rtl8192u: ieee80211: Replace snprintf with scnprintf

staging: rtl8192u: ieee80211: Replace snprintf with scnprintf

When the number of bytes to be printed exceeds the limit snprintf
returns the number of bytes that would have been printed (if there was
no truncation). This might cause issues, hence use scnprintf which
returns the actual number of bytes printed to buffer always.

Signed-off-by: Rohit Sarkar <rohitsarkar5398@gmail.com>
Link: https://lore.kernel.org/r/20190910182415.GA5768@SARKAR
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>