ARM: 8799/1: mm: fix pci_ioremap_io() offset check

IO_SPACE_LIMIT is the ending address of the PCI IO space, i.e
something like 0xfffff (and not 0x100000).

Therefore, when offset = 0xf0000 is passed as argument, this function
fails even though the offset + SZ_64K fits below the
IO_SPACE_LIMIT. This makes the last chunk of 64 KB of the I/O space
not usable as it cannot be mapped.

This patch fixes that by substracing 1 to offset + SZ_64K, so that we
compare the addrss of the last byte of the I/O space against
IO_SPACE_LIMIT instead of the address of the first byte of what is
after the I/O space.

Fixes: c2794437 ("ARM: Add fixed PCI i/o mapping")
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>