spi: Fix typo on SPI_MEM help text

The correct form is "a high-level", so fix it accordingly.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -52,7 +52,7 @@ config SPI_MEM
 	help
 	  Enable this option if you want to enable the SPI memory extension.
 	  This extension is meant to simplify interaction with SPI memories
-	  by providing an high-level interface to send memory-like commands.
+	  by providing a high-level interface to send memory-like commands.
 
 comment "SPI Master Controller Drivers"