net: dsa: ksz: Make reg_mib_cnt a u8 as it never exceeds 255

Currently the for-loop in ksz8_port_init_cnt is causing a static
analysis infinite loop warning with the comparison of
mib->cnt_ptr < dev->reg_mib_cnt. This occurs because mib->cnt_ptr
is a u8 and dev->reg_mib_cnt is an int and the analyzer determines
that mib->cnt_ptr potentially can wrap around to zero if the value
in dev->reg_mib_cnt is > 255. However, this value is never this
large, it is always less than 256 so make reg_mib_cnt a u8.

Addresses-Coverity: ("Infinite loop")
Fixes: e66f840c ("net: dsa: ksz: Add Microchip KSZ8795 DSA driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210428120010.337959-1-colin.king@canonical.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/microchip/ksz_common.h

@@ -69,7 +69,7 @@ struct ksz_device {
 	int cpu_ports;			/* port bitmap can be cpu port */
 	int phy_port_cnt;
 	int port_cnt;
-	int reg_mib_cnt;
+	u8 reg_mib_cnt;
 	int mib_cnt;
 	const struct mib_names *mib_names;
 	phy_interface_t compat_interface;