nvme: don't always build constants.o

The entire content of constants.c if guarded by an ifdef, so switch to
just building the file conditionally instead.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Keith Busch <[e-mail]>
Reviewed-by: Chaitanya Kulkarni <[e-mail]>
Reviewed-by: Sagi Grimberg <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/nvme/host/Makefile

···
 obj-$(CONFIG_NVME_TCP)			+= nvme-tcp.o
 obj-$(CONFIG_NVME_APPLE)		+= nvme-apple.o
 
-nvme-core-y				:= core.o ioctl.o constants.o
+nvme-core-y				+= core.o ioctl.o
+nvme-core-$(CONFIG_NVME_VERBOSE_ERRORS)	+= constants.o
 nvme-core-$(CONFIG_TRACING)		+= trace.o
 nvme-core-$(CONFIG_NVME_MULTIPATH)	+= multipath.o
 nvme-core-$(CONFIG_BLK_DEV_ZONED)	+= zns.o

drivers/nvme/host/constants.c

···
 
 #include "nvme.h"
 
-#ifdef CONFIG_NVME_VERBOSE_ERRORS
 static const char * const nvme_ops[] = {
 	[nvme_cmd_flush] = "Flush",
 	[nvme_cmd_write] = "Write",
···
 		return nvme_admin_ops[opcode];
 	return "Unknown";
 }
-#endif /* CONFIG_NVME_VERBOSE_ERRORS */