mlxbf-bootctl: use sysfs_emit_at() in secure_boot_fuse_state_show()

mlxbf-bootctl: use sysfs_emit_at() in secure_boot_fuse_state_show()

A warning is seen when running the latest kernel on a BlueField SOC:
[251.512704] ------------[ cut here ]------------
[251.512711] invalid sysfs_emit: buf:0000000003aa32ae
[251.512720] WARNING: CPU: 1 PID: 705264 at fs/sysfs/file.c:767 sysfs_emit+0xac/0xc8

The warning is triggered because the mlxbf-bootctl driver invokes
"sysfs_emit()" with a buffer pointer that is not aligned to the
start of the page. The driver should instead use "sysfs_emit_at()"
to support non-zero offsets into the destination buffer.

Fixes: 9886f575de5a ("platform/mellanox: mlxbf-bootctl: use sysfs_emit() instead of sprintf()")
Signed-off-by: David Thompson <davthompson@nvidia.com>
Link: https://lore.kernel.org/r/20250407132558.2418719-1-davthompson@nvidia.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>