platform/x86: dell_rbu: fix assignment in if condition warning

platform/x86: dell_rbu: fix assignment in if condition warning

Refactor to remove assignments from inside if conditions, as required
by kernel coding style. This improves code readability and resolves
checkpatch.pl warnings:

    ERROR: do not use assignment in if condition

Signed-off-by: Darshan Rathod <darshanrathod475@gmail.com>
Link: https://lore.kernel.org/r/20250801104705.1824495-1-darshanrathod475@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>