Commit "serial/arc-uart: split probe from probe_earlyprintk" introduced
a build time warning:
"WARNING: vmlinux.o(.data+0x5baa0): Section mismatch in reference from
the variable early_arc_platform_driver to the function
.init.text:arc_serial_probe_earlyprintk()"
While at it - fixed another incorrectly placed initdata annotation.