Staging: rtl8192e: rtl_core.c: Remove unused variable

This patch discards the variable ResetThreshold as it is not used
anywhere throughout the kernel.

Build tested it.

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>