u-boot-imx: Fix filename at install

u-boot-imx: Fix filename at install

Fix the error:

er/build/tmp/work/imx8mqevk-fslc-linux/imx-boot/0.2-r0/git/iMX8M
| cp: cannot stat '/media/daiane/TRIFORCE/yocto/master/build/tmp/deploy/images/imx8mqevk/imx-boot-tools/u-boot-nodtb.bin': No such file or directory
| WARNING: exit code 1 from a shell command.
| ERROR: Function failed: do_compile (log file is located at /media/daiane/TRIFORCE/yocto/master/build/tmp/work/imx8mqevk-fslc-linux/imx-boot/0.2-r0/temp/log.do_compile.27338)

Signed-off-by: Daiane Angolini <daiane.angolini@nxp.com>