Staging: rtl8712: fix math errors in snprintf()

The original code had calls to snprintf(p, 7, "wpa_ie=") but that string
is 8 characters (because snprintf() puts a NUL terminator on the end).
So instead of an '=' the what gets written to buf is a NUL terminator
followed by the rest of the string.

And actually the %02x formats are three chars as well when you include
the terminator.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>