NFC: pn533: Remove pointless flags param

__pn533_send_cmd_frame_async() is called when lock is held so GFP_KERNEL
flag will be always used. Thus, having extra param does not optimise the
code.

Signed-off-by: Waldemar Rymarkiewicz <waldemar.rymarkiewicz@tieto.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>