powerpc/8xx: Remove left-over instruction and comments in DataStoreTLBMiss handler

Commit ac9f97ff8b32 ("powerpc/8xx: Inconditionally use task PGDIR in
DTLB misses") removed the test that needed the valeur in SPRN_EPN but
failed to remove the read.

Remove it.

And remove related comments, including the very same comment
in InstructionTLBMiss that should have been removed by
commit 33c527522f39 ("powerpc/8xx: Inconditionally use task PGDIR in
ITLB misses").

Also update the comment about absence of a second level table which
has been handled implicitely since commit 5ddb75cee5af ("powerpc/8xx:
remove tests on PGDIR entry validity").

Fixes: ac9f97ff8b32 ("powerpc/8xx: Inconditionally use task PGDIR in DTLB misses")
Signed-off-by: Christophe Leroy <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/5811c8d1[e-mail]

arch/powerpc/kernel/head_8xx.S

···
  * For the MPC8xx, this is a software tablewalk to load the instruction
  * TLB.  The task switch loads the M_TWB register with the pointer to the first
  * level table.
- * If we discover there is no second level table (value is zero) or if there
+ * If there is no second level table (value is zero) or if there
  * is an invalid pte, we load that into the TLB, which causes another fault
  * into the TLB Error interrupt where we can handle such problems.
  * We have to use the MD_xxx registers for the tablewalk because the
···
 	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mtspr	SPRN_M_TW, r11
 
-	/* If we are faulting a kernel address, we have to use the
-	 * kernel page tables.
-	 */
 	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
 	INVALIDATE_ADJACENT_PAGES_CPU15(r10, r11)
 	mtspr	SPRN_MD_EPN, r10
···
 	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mtspr	SPRN_M_TW, r11
 
-	/* If we are faulting a kernel address, we have to use the
-	 * kernel page tables.
-	 */
-	mfspr	r10, SPRN_MD_EPN
 	mfspr	r10, SPRN_M_TWB	/* Get level 1 table */
 	lwz	r11, 0(r10)	/* Get level 1 entry */