regcache: Mark cache dirty if selector register rewrite fails

After a successful cache synchronization, regcache_sync() clears
cache_dirty. If rewriting a selector register later fails, the cache
and hardware become inconsistent while the cache still appears clean.

Update cache_dirty to reflect the cache and hardware state when
selector register rewriting fails.

Signed-off-by: bui duc phuc <phucduc.bui@gmail.com>
Link: https://patch.msgid.link/20260713050312.38729-3-phucduc.bui@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>