staging: rtl8192u: simplify rtl819x_evm_dbtopercentage()

Use clamp() to simplify function rtl819x_evm_dbtopercentage() and
reduce object file size.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20200118195305.16685-2-straube.linux@gmail.com


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