powerpc/8xx: Remove offset in SPRN_M_TWB

powerpc/8xx: Remove offset in SPRN_M_TWB

SPRN_M_TWB contains the address of task PGD minus an offset which
compensates the offset required when accessing the kernel PGDIR.
However, since commit ac9f97ff8b32 ("powerpc/8xx: Inconditionally use
task PGDIR in DTLB misses") and commit 33c527522f39 ("powerpc/8xx:
Inconditionally use task PGDIR in ITLB misses") kernel PGDIR is not
used anymore in hot paths.

Remove this offset which was added by
commit fde5a9057fcf ("powerpc/8xx: Optimise access to swapper_pg_dir")

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[maddy: Fixed checkpatch.pl warning for "pathes"]
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/9710d960b512996e64beebfd368cfeaadb28b3ba.1755509047.git.christophe.leroy@csgroup.eu