staging: rtl8192u: fix return statements in r8192U_core.c

This patch fixes the following checkpatch error:
ERROR: return is not a function, parentheses are not required

Also, fixes the spaces in return statements to
improve code readability.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>