MIPS: generic: Fix machine compatible matching

We now have a platform (Ranchu) in the "generic" platform which matches
based on the FDT compatible string using mips_machine_is_compatible(),
however that function doesn't stop at a blank struct
of_device_id::compatible as that is an array in the struct, not a
pointer to a string.

Fix the loop completion to check the first byte of the compatible array
rather than the address of the compatible array in the struct.

Fixes: eed0eabd ("MIPS: generic: Introduce generic DT-based board support")
Signed-off-by: James Hogan <jhogan@kernel.org>
Reviewed-by: Paul Burton <paul.burton@mips.com>
Reviewed-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18580/

arch/mips/include/asm/machine.h

@@ -52,7 +52,7 @@ mips_machine_is_compatible(const struct mips_machine *mach, const void *fdt)
 	if (!mach->matches)
 		return NULL;
 
-	for (match = mach->matches; match->compatible; match++) {
+	for (match = mach->matches; match->compatible[0]; match++) {
 		if (fdt_node_check_compatible(fdt, 0, match->compatible) == 0)
 			return match;
 	}