powerpc/sstep: Fix incorrect return from analyze_instr()

We currently just percolate the return value from analyze_instr()
to the caller of emulate_step(), especially if it is a -1.

For one particular case (opcode = 4) for instructions that aren't
currently emulated, we are returning 'should not be single-stepped'
while we should have returned 0 which says 'did not emulate, may
have to single-step'.

Fixes: 930d6288a26787 ("powerpc: sstep: Add support for maddhd, maddhdu, maddld instructions")
Signed-off-by: Ananth N Mavinakayanahalli <[e-mail]>
Suggested-by: Michael Ellerman <[e-mail]>
Tested-by: Naveen N. Rao <[e-mail]>
Reviewed-by: Sandipan Das <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/lib/sstep.c

···
 
 #ifdef __powerpc64__
 	case 4:
+		/*
+		 * There are very many instructions with this primary opcode
+		 * introduced in the ISA as early as v2.03. However, the ones
+		 * we currently emulate were all introduced with ISA 3.0
+		 */
 		if (!cpu_has_feature(CPU_FTR_ARCH_300))
 			goto unknown_opcode;
 
···
 		 * There are other instructions from ISA 3.0 with the same
 		 * primary opcode which do not have emulation support yet.
 		 */
-		return -1;
+		goto unknown_opcode;
 #endif
 
 	case 7:		/* mulli */