staging: vt6655: removed incorrect casting in wpactl.c

This patch fixes the following type of sparse warnings:

drivers/staging/vt6655/wpactl.c:596:47: warning: cast from restricted gfp_t
drivers/staging/vt6655/wpactl.c:638:68: warning: cast from restricted gfp_t
drivers/staging/vt6655/wpactl.c:860:42: warning: cast from restricted gfp_t

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>