staging: rtl8723au: fix sparse warning

staging: rtl8723au: fix sparse warning

Found running sparse on the rtl8723au driver.

  CHECK   drivers/staging/rtl8723au/core/rtw_cmd.c
drivers/staging/rtl8723au/core/rtw_cmd.c:1479:54: warning: incorrect type in argument 2 (different base types)
drivers/staging/rtl8723au/core/rtw_cmd.c:1479:54:    expected int [signed] gfp
drivers/staging/rtl8723au/core/rtw_cmd.c:1479:54:    got restricted gfp_t

Signed-off-by: Clement Calmels <clement.calmels@free.fr>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>