If you running linux on the module you can dump any partition to a file:
# cat /dev/mtdX > imageX.img
Where X is a partition number from flpart. so du dum kernel do:
# cat /dev/mtd2 > image2.img
then ftp image2.img in to your host - this is basically your uImage file
To see if you can do it from u-boot check uboot manual here
U-Boot Reference Manual
but saving it to a file might be tricky if possible at all. reverse engineering is not intention of u-boot. Why do you want to read kernel in to a file?