staging: rtl8192u: Fix checkpatch issue with comma in r819xU_firmware.c

Add space after ',' to fix the error message provided by checkpatch.pl:
ERROR: space required after that ','

Signed-off-by: Freeman Zhang <freeman.zhang1992@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>