powerpc/ptrace: Consolidate reg index calculation

Today we have:

	#ifdef CONFIG_PPC32
		index = addr >> 2;
		if ((addr & 3) || child->thread.regs == NULL)
	#else
		index = addr >> 3;
		if ((addr & 7))
	#endif

sizeof(long) has value 4 for PPC32 and value 8 for PPC64.

Dividing by 4 is equivalent to >> 2 and dividing by 8 is equivalent
to >> 3.

And 3 and 7 are respectively (sizeof(long) - 1).

Use sizeof(long) to get rid of the #ifdef CONFIG_PPC32 and consolidate
the calculation and checking.

thread.regs have to be not NULL on both PPC32 and PPC64 so adding
that test on PPC64 is harmless.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3cd1e284e93c60db981659585e18d1f6bb73ed2f.1597770847.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/ptrace/ptrace.c

@@ -55,14 +55,9 @@ long arch_ptrace(struct task_struct *child, long request,
 
 		ret = -EIO;
 		/* convert to index and check */
-#ifdef CONFIG_PPC32
-		index = addr >> 2;
-		if ((addr & 3) || (index > PT_FPSCR)
+		index = addr / sizeof(long);
+		if ((addr & (sizeof(long) - 1)) || (index > PT_FPSCR)
 		    || (child->thread.regs == NULL))
-#else
-		index = addr >> 3;
-		if ((addr & 7) || (index > PT_FPSCR))
-#endif
 			break;
 
 		CHECK_FULL_REGS(child->thread.regs);
@@ -90,14 +85,9 @@ long arch_ptrace(struct task_struct *child, long request,
 
 		ret = -EIO;
 		/* convert to index and check */
-#ifdef CONFIG_PPC32
-		index = addr >> 2;
-		if ((addr & 3) || (index > PT_FPSCR)
+		index = addr / sizeof(long);
+		if ((addr & (sizeof(long) - 1)) || (index > PT_FPSCR)
 		    || (child->thread.regs == NULL))
-#else
-		index = addr >> 3;
-		if ((addr & 7) || (index > PT_FPSCR))
-#endif
 			break;
 
 		CHECK_FULL_REGS(child->thread.regs);