MIPS: Lantiq: Fix another request_mem_region() return code check

Hauke already fixed a couple of them, but one instance remains
that checks for a negative integer when it should check
for a NULL pointer:

arch/mips/lantiq/xway/sysctrl.c: In function 'ltq_soc_init':
arch/mips/lantiq/xway/sysctrl.c:473:19: error: ordered comparison of pointer with integer zero [-Werror=extra]

Fixes: 6e807852676a ("MIPS: Lantiq: Fix check for return value of request_mem_region()")
Signed-off-by: Arnd Bergmann <[e-mail]>
Cc: John Crispin <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/15043/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/lantiq/xway/sysctrl.c

···
 			panic("Failed to load xbar nodes from devicetree");
 		if (of_address_to_resource(np_pmu, 0, &res_xbar))
 			panic("Failed to get xbar resources");
-		if (request_mem_region(res_xbar.start, resource_size(&res_xbar),
-			res_xbar.name) < 0)
+		if (!request_mem_region(res_xbar.start, resource_size(&res_xbar),
+			res_xbar.name))
 			panic("Failed to get xbar resources");
 
 		ltq_xbar_membase = ioremap_nocache(res_xbar.start,