regcache: Do not overwrite error code when finalizing cache after error

During regcache initialization, if an error occurs in the
cache_ops->populate callback, and if cache operations include an exit
callback, the error code from populate() is overwritten with the return
value from exit(). This hides the error condition from the caller of
regcache_init(), and can cause NULL pointer dereferences when the regcache
is later accessed.

Fixes: 94a3a95f0315 ("regcache: Add ->populate() callback to separate from ->init()")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Link: https://patch.msgid.link/20260616114429.1852456-1-flavra@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>