hw/mcf5206: Fix buffer overflow for MBAR read / write

Report from smatch:

mcf5206.c:384 m5206_mbar_readb(7) error: buffer overflow 'm5206_mbar_width' 128 <= 128
mcf5206.c:403 m5206_mbar_readw(8) error: buffer overflow 'm5206_mbar_width' 128 <= 128
mcf5206.c:427 m5206_mbar_readl(8) error: buffer overflow 'm5206_mbar_width' 128 <= 128
mcf5206.c:451 m5206_mbar_writeb(9) error: buffer overflow 'm5206_mbar_width' 128 <= 128
mcf5206.c:475 m5206_mbar_writew(9) error: buffer overflow 'm5206_mbar_width' 128 <= 128
mcf5206.c:503 m5206_mbar_writel(9) error: buffer overflow 'm5206_mbar_width' 128 <= 128

m5206_mbar_width has 0x80 elements and supports 0 <= offset < 0x200.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
