soc: qcom: spcom: fix section mismatch warning

The KASAN builds have started producing the warning:
WARNING: vmlinux.o(.text+0x8cad78): Section mismatch in reference from the function spcom_probe() to the function .init.text:spcom_register_chardev()
The function spcom_probe() references
the function __init spcom_register_chardev().
This is often because spcom_probe lacks a __init
annotation or the annotation of spcom_register_chardev is wrong.

Indeed, spcom_register_chardev is called from the non-__init
spcom_probe, so marking spcom_register_chardev __init is dangerous.

Bug: 139442076
Change-Id: I8feff354bcea8171d8f8130cfa8a230439efc9b0
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>