mfd: syscon: Return -EPROBE_DEFER if the syscon is not found

mfd: syscon: Return -EPROBE_DEFER if the syscon is not found

These days we can register syscons with of_syscon_register_regmap() so
when we can't find the syscon that probably means it hasn't been
registered yet.  Return -EPROBE_DEFER so the driver will try probing
again.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Chen-Yu Tsai <wens@kernel.org>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/aQdHmrchkmOr34r3@stanley.mountain
Signed-off-by: Lee Jones <lee@kernel.org>