staging: wilc1000: replace 'ptr > 0' check by 'ptr' check.

This silences a sparse warning about incompatible comparisons, while making the
intent of the check a bit clearer.

Signed-off-by: Mario J. Rugiero <mrugiero@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>