serial: qcom-geni: Fix off-by-one error in ida_alloc_range()

The ida_alloc_range() function expects an inclusive range, meaning both
the start and end values are valid allocation targets. Passing nr_ports
as the upper bound allows allocation of an ID equal to nr_ports, which
is out of bounds when used as an index into the port array.

Fix this by subtracting 1 from nr_ports in both calls to ida_alloc_range(),
ensuring the allocated ID stays within the valid range
[start, nr_ports - 1].

This prevents potential out-of-bounds access when the allocated ID is used
as an index.

Fixes: 9391ab1 ("serial: qcom-geni: Make UART port count configurable via Kconfig")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202508180815.R2nDyajs-lkp@intel.com/
Signed-off-by: Zong Jiang <quic_zongjian@quicinc.com>
Link: https://lore.kernel.org/r/20250827120319.1682835-1-quic_zongjian@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Zong Jiang

drivers/tty/serial/qcom_geni_serial.c

@@ -271,9 +271,11 @@ static struct qcom_geni_serial_port *get_port_from_line(int line, bool console,
 		int max_alias_num = of_alias_get_highest_id("serial");
 
 		if (line < 0 || line >= nr_ports)
-			line = ida_alloc_range(&port_ida, max_alias_num + 1, nr_ports, GFP_KERNEL);
+			line = ida_alloc_range(&port_ida, max_alias_num + 1,
+					       nr_ports - 1, GFP_KERNEL);
 		else
-			line = ida_alloc_range(&port_ida, line, nr_ports, GFP_KERNEL);
+			line = ida_alloc_range(&port_ida, line,
+					       nr_ports - 1, GFP_KERNEL);
 
 		if (line < 0)
 			return ERR_PTR(-ENXIO);