staging: rtl8712: simplify evm_db2percentage()

Use clamp() to simplify function evm_db2percentage() and reduce object
file size.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20200118195305.16685-3-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>