staging: goldfish: (coding style) Rewrite comparisons to NULL as "!data->reg_base"

Rewrite comparisons to NULL "data->reg_base == NULL" as "!data->reg_base" to conform to checkpatch.

Signed-off-by: Christian Colic <colic.christian@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>