spi: spi-mem: Fix build error without CONFIG_SPI_MEM

When building with CONFIG_SPI_MEM is not set
gc warns this:

drivers/spi/spi-zynq-qspi.o: In function `zynq_qspi_supports_op':
spi-zynq-qspi.c:(.text+0x1da): undefined reference to `spi_mem_default_supports_op'

Fixes: 67dca5e5 ("spi: spi-mem: Add support for Zynq QSPI controller")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi-mem.h

@@ -295,6 +295,10 @@ int spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
 void spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
 					  const struct spi_mem_op *op,
 					  struct sg_table *sg);
+
+bool spi_mem_default_supports_op(struct spi_mem *mem,
+				 const struct spi_mem_op *op);
+
 #else
 static inline int
 spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
@@ -310,6 +314,13 @@ spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
 				     struct sg_table *sg)
 {
 }
+
+bool spi_mem_default_supports_op(struct spi_mem *mem,
+				 const struct spi_mem_op *op)
+{
+	return false;
+}
+
 #endif /* CONFIG_SPI_MEM */
 
 int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op);
@@ -341,9 +352,6 @@ int spi_mem_driver_register_with_owner(struct spi_mem_driver *drv,
 
 void spi_mem_driver_unregister(struct spi_mem_driver *drv);
 
-bool spi_mem_default_supports_op(struct spi_mem *mem,
-				 const struct spi_mem_op *op);
-
 #define spi_mem_driver_register(__drv)                                  \
 	spi_mem_driver_register_with_owner(__drv, THIS_MODULE)