Staging: vt6655: Eliminate nested if else

Eliminate  nested if else statement, reduce code duplication, and
shorten long lines by creating a new variable, len, to determine
function input needed for s_uGetTxRsvTime.

Signed-off-by: Briana Oursler <briana.oursler@gmail.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Link: https://lore.kernel.org/r/301ff66e13e76be6416b5c0f8359249fa25f08e3.1585763457.git.briana.oursler@gmail.com


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