tty: mxser: remove redundant assignment to hwid

tty: mxser: remove redundant assignment to hwid

The variable hwid is assigned a value but it is never read. The
assignment is redundant and can be removed.

Cleans up clang scan build warning:
drivers/tty/mxser.c:401:7: warning: Although the value stored to 'hwid'
is used in the enclosing expression, the value is never actually read
from 'hwid' [deadcode.DeadStores]

Acked-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220730130925.150018-1-colin.i.king@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>