target/ppc: fix typo in SIMM5 extraction helper

As the macro name suggests, the argument should be signed and not unsigned.
Signed-off-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

target/ppc/internal.h

@@ -124,7 +124,7 @@ EXTRACT_SHELPER(SIMM, 0, 16);
 /* 16 bits unsigned immediate value */
 EXTRACT_HELPER(UIMM, 0, 16);
 /* 5 bits signed immediate value */
-EXTRACT_HELPER(SIMM5, 16, 5);
+EXTRACT_SHELPER(SIMM5, 16, 5);
 /* 5 bits signed immediate value */
 EXTRACT_HELPER(UIMM5, 16, 5);
 /* 4 bits unsigned immediate value */