rtlwifi: btcoexist: Fix "always true" warning from commit ed364abf

The 0-DAY kernel build testing backend reports the following warning:
drivers/net/wireless/rtlwifi/btcoexist/halbtcoutsrc.c:516 halbtc_bitmask_write_1byte()
warn: always true condition '(bit_mask != 4294967295) => (0-255 != u32max)'

This problem was introduced in commit ed364abf,
and arises because the caller of halbtc_bitmask_write_1byte() is using a
u8 rather than a u32 for the data.

Reported-by: Kbuild test robot <kbuild-all@01.org>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Kbuild test robot <kbuild-all@01.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>