tty: serial: jsm: fix two assignments in if conditions

Fixes two warnings reported of the form
"ERROR: do not use assignment in if condition"
reported by checkpatch.pl.

Signed-off-by: Alexander Vorwerk <alexander.vorwerk@stud.uni-goettingen.de>
Link: https://lore.kernel.org/r/20220315020745.15752-1-alexander.vorwerk@stud.uni-goettingen.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>