mfd: core: Improve compile coverage of mfd_match_of_node_to_dev()

mfd: core: Improve compile coverage of mfd_match_of_node_to_dev()

As of commit c7fe3bbfd622b5ee ('mfd: core: Use of_property_read_reg() to
parse "reg"'), all code in mfd_match_of_node_to_dev() compiles fine when
CONFIG_OF is disabled.  As the sole caller of this function is
protected by IS_ENABLED(CONFIG_OF), the #ifdef inside the function can
be removed to increase build coverage, without impacting code size.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/7b9a4a355c5da3fe812ead663285d05b64b84857.1764320964.git.geert+renesas@glider.be
Signed-off-by: Lee Jones <lee@kernel.org>