kernel/linux: fix fall-out due to arm64 special case

Cset 3b61be3d7aa6 (prepare for arch whose kenel name is not the standard name)
failed to name a variable consistently, so all archs but arm64 were broken.

Fix that by renaming the variable in a consistent way.

Reported-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 CT_LOCAL_TARBALLS_DIR="${HOME}/src"

 CT_SAVE_TARBALLS=y

 CT_LOG_EXTRA=y

 CT_ARCH_LE=y

 CT_ARCH_FLOAT_SW=y

 CT_ARCH_mips=y

 CT_TARGET_VENDOR="sde"

 CT_BINUTILS_V_2_21_1a=y

 CT_CC_V_4_4_6=y

 # CT_CC_GCC_ENABLE_TARGET_OPTSPACE is not set

 CT_LIBC_none=y

 CT_DEBUG_gdb=y

 CT_GDB_V_6_8a=y

 CT_GMP_V_4_3_2=y

 CT_MPFR_V_2_4_2=y

 CT_PPL_V_0_10_2=y

 CT_CLOOG_V_0_15_10=y