mfd: qcom_rpm: Use devm_of_platform_populate() to simplify code

Use devm_of_platform_populate() instead of hand-writing it.
This simplifies the code.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/fd997dc92b9cee219e9c55e22959a94f4bbf570b.1668949256.git.christophe.jaillet@wanadoo.fr