The debug code in sh_pfc_write_config_reg() prints the width of the
field being modified.

However, registers with a variable-width field layout are identified by
pinmux_cfg_reg.field_width being zero, hence zeroes are printed instead
of the actual field widths.

Fix this by printing the Hamming weight of the field mask instead, which
is correct for both fixed-width and variable-width fields.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>