memory: omap-gpmc: Delete an unnecessary check before the function call "gpiochip_free_own_desc"

The gpiochip_free_own_desc() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Roger Quadros <rogerq@ti.com>