iwlwifi: out-of-bounds access in iwl_init_sband_channels

KASan error report:
==================================================================
BUG: KASan: out of bounds access in iwl_init_sband_channels+0x207/0x260 [iwlwifi] at addr ffff8800c2d0aac8
Read of size 4 by task modprobe/329
==================================================================

Both loops of this function compare data from the 'chan' array and then
check if the index is valid.

The 2 conditions should be inverted to avoid an out-of-bounds access.

Signed-off-by: Adrien Schildknecht <adrien+dev@schischi.me>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>