powerpc/vdso32: Fallback on getres syscall when clock is unknown

There are other clocks than the standard ones, for instance
per process clocks. Therefore, being above the last standard clock
doesn't mean it is a bad clock. So, fallback to syscall instead
of returning -EINVAL inconditionaly.

Fixes: e33ffc9 ("powerpc/vdso32: implement clock_getres entirely")
Cc: [email protected] # v5.6+
Reported-by: Aurelien Jarno <[email protected]>
Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Tested-by: Aurelien Jarno <[email protected]>
Link: https://lore.kernel.org/r/7316a9e2c0c2517923eb4b0411c4a08d15e675a4.1589017281.git.christophe.leroy@csgroup.eu

Author: chleroy

arch/powerpc/kernel/vdso32/gettimeofday.S

@@ -218,11 +218,11 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
 	blr
 
 	/*
-	 * invalid clock
+	 * syscall fallback
 	 */
 99:
-	li	r3, EINVAL
-	crset	so
+	li	r0,__NR_clock_getres
+	sc
 	blr
   .cfi_endproc
 V_FUNCTION_END(__kernel_clock_getres)