x86/platform/olpc: Remove unused variable 'len' in olpc_dt_compatible_match()

The following build warning highlights some unused code:

  arch/x86/platform/olpc/olpc_dt.c: In function ‘olpc_dt_compatible_match’:
  arch/x86/platform/olpc/olpc_dt.c:222:12: warning: variable ‘len’ set but not used [-Wunused-but-set-variable]

The compiler is right, the local variable 'len' is set but never used,
so remove it.

Fixes: a7a9bacb ("x86/platform/olpc: Use a correct version when making up a battery node")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20241025074203.1921344-1-zengheng4@huawei.com