[PATCH] Serial: Fix small CONFIG_SERIAL_8250_NR_UARTS

If CONFIG_SERIAL_8250_NR_UARTS is smaller than the array size in
asm/serial.h, we trampled on memory which wasn't ours.  Take our
big boots away by limiting the number of ports initialised to the
smaller of ...NR_UARTS and the array size.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>