serial: bcm63xx_uart: fix compilation after "TTY: switch tty_insert_flip_char"

92a19f9c

 introduced a local variable
with the same name as the argument to bcm_uart_do_rx, breaking
compilation. Fix this by renaming the new variable and its uses where
expected.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>