staging: rtl8192u: remove unneeded compiler flags

-std=gnu89 is specified by the top Makefile. Adding it in a driver
Makefile is redundant.

A driver should avoid specifying the optimization flag.
-O2, -O3, or -Os is passed by the top Makefile based on the
CONFIG_CC_OPTIMIZE_FOR_* option.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20200104162136.19170-3-masahiroy@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/Makefile

 # SPDX-License-Identifier: GPL-2.0
 NIC_SELECT = RTL8192U
 
-ccflags-y := -std=gnu89
-ccflags-y += -O2
-
 ccflags-y += -DCONFIG_FORCE_HARD_FLOAT=y
 ccflags-y += -DJACKSON_NEW_8187 -DJACKSON_NEW_RX
 ccflags-y += -DTHOMAS_BEACON -DTHOMAS_TASKLET -DTHOMAS_SKB -DTHOMAS_TURBO