Fix warnings reported by smatch by initializing local 'ret' variable
to 0.

drivers/base/regmap/regcache-maple.c:186 regcache_maple_drop()
error: uninitialized symbol 'ret'.
drivers/base/regmap/regcache-maple.c:290 regcache_maple_sync()
error: uninitialized symbol 'ret'.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: f033c26d ("regmap: Add maple tree based register cache")
Link: https://lore.kernel.org/r/20240329144630.1965159-1-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>