soc/amd/phoenix/Kconfig: use lower case hex digits in VGA_BIOS_ID

cbfs_boot_map_optionrom will generate lower case hex digits for the
filename to look for in CBFS, so make sure that the file name will use
lower case hex digits and no upper case hex digits.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I1d4daa04120de0f2c853a44691b7e2c52eb2af20
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75483
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/amd/phoenix/Kconfig b/src/soc/amd/phoenix/Kconfig
index 4efe5c9..adb990b 100644
--- a/src/soc/amd/phoenix/Kconfig
+++ b/src/soc/amd/phoenix/Kconfig
@@ -249,7 +249,7 @@
 
 config VGA_BIOS_ID
 	string
-	default "1002,15BF"
+	default "1002,15bf"
 	help
 	  The default VGA BIOS PCI vendor/device ID should be set to the
 	  result of the map_oprom_vendev() function in graphics.c.