Fix the bit field width information for the IPSR4 register
in the r8a7779 pin function controller (PFC).

Without this fix the Marzen board fails to receive data
over the serial console due to misconfigured pin function
for the RX pin.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Tested-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: NSimon Horman <horms@verge.net.au>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>