sdk: fix search for dynamic loader

if the package "nativesdk-glibc-dbg" is installed as part of the SDK,
the existing search expression finds two files:

$OECORE_NATIVE_SYSROOT/lib/.debug/ld-linux-x86-64.so.2
$OECORE_NATIVE_SYSROOT/lib/ld-linux-x86-64.so.2

The generated relocate_sdk.sh shell script contains then an extra
newline and segfaults during SDK relocation.

Limit the search depth to 1, to avoid finding the file in the .debug
directory.

Signed-off-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>