proc: fixup uptime selftest

syscall(3) returns -1 and sets errno on error, unlike "syscall"
instruction.

Systems which have <= 32/64 CPUs are unaffected. Test won't bounce
to all CPUs before completing if there are more of them.

Link: https://lkml.kernel.org/r/Y1bUiT7VRXlXPQa1@p183
Fixes: 1f5bd0547654 ("proc: selftests: test /proc/uptime")
Signed-off-by: Alexey Dobriyan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/proc/proc-uptime-002.c

···
 // while shifting across CPUs.
 #undef NDEBUG
 #include <assert.h>
+#include <errno.h>
 #include <unistd.h>
 #include <sys/syscall.h>
 #include <stdlib.h>
···
 		len += sizeof(unsigned long);
 		free(m);
 		m = malloc(len);
-	} while (sys_sched_getaffinity(0, len, m) == -EINVAL);
+	} while (sys_sched_getaffinity(0, len, m) == -1 && errno == EINVAL);
 
 	fd = open("/proc/uptime", O_RDONLY);
 	assert(fd >= 0);