serial: linflexuart: drop the unneeded stack variable

In commit a7823395 ("tty: serial: linflexuart: UART support for FIFO
with DMA"), the second param of linflex_console_putchar() has been updated
to "unsigned char" to compatible with v6.1 kernel, then the ich variable in
linflex_poll_putchar() is not needed anymore, so drop it.

Signed-off-by: Zhantao Tang <zhantao.tang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>