wifi: iwlwifi: cfg: Limit cb_size to valid range

wifi: iwlwifi: cfg: Limit cb_size to valid range

on arm64 defconfig build failed with gcc-8:

drivers/net/wireless/intel/iwlwifi/pcie/ctxt-info.c:208:3:
include/linux/bitfield.h:195:3: error: call to '__field_overflow'
declared with attribute error: value doesn't fit into mask
   __field_overflow();     \
   ^~~~~~~~~~~~~~~~~~
include/linux/bitfield.h:215:2: note: in expansion of macro '____MAKE_OP'
  ____MAKE_OP(u##size,u##size,,)
  ^~~~~~~~~~~
include/linux/bitfield.h:218:1: note: in expansion of macro '__MAKE_OP'
 __MAKE_OP(32)

Limit cb_size to valid range to fix it.

Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Link: https://patch.msgid.link/7b373a4426070d50b5afb3269fd116c18ce3aea8.1748332709.git.xiaopei01@kylinos.cn
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>